SAN FRANCISCO — Military helicopters delivered testing kits Thursday to a cruise ship being held off the coast of California, as officials in Washington faced angry questions about whether the vessel is set to become the latest breeding ground for the deadly novel coronavirus.

The Grand Princess, which was returning to San Francisco after a two-week cruise to Hawaii, remained offshore and in limbo at the request of California Gov. Gavin Newsom (D). About 100 people were expected to be tested, among them 11 passengers and 10 crew members who have shown potential signs of covid-19, the respiratory disease caused by the coronavirus. Results were expected Friday.

The fraught situation was the latest in an outbreak marked by confusion and uncertainty. As the U.S. death toll rose to 12 on Thursday and the virus spread to new states — including three cases in Montgomery County, Md. — the stock market again plunged. Congress passed an $8.3 billion emergency spending bill aimed at helping the nation wrestle with the growing crisis.

Even as the military ferried tests to the cruise ship and thousands of passengers waited uneasily on board, public health officials on land were investigating a cluster of coronavirus cases among the roughly 2,500 people who had taken an earlier cruise on the same ship. One of those passengers, a 71-year-old man, has since died of covid-19.

Princess Cruises said in a statement that it is working with local authorities and the Centers for Disease Control and Prevention to identify “groups of guests and crew who will be tested before arrival into San Francisco.” Among them were 62 passengers who had been on the previous cruise and stayed aboard for the trip to Hawaii.

In a phone call from the ship, Wray McClelland, 55, said he and his wife were among those who cruised to both Mexico and Hawaii — a group that the CDC has said needs to be tested. The couple have been confined to their room since early Wednesday morning, when they were told to wait for the ship’s medical team to contact them. Thursday night, they were still waiting. When McClelland, of British Columbia, heard the captain announce over loudspeakers that testing had been completed, he got worried.

“We started to panic,” he said. “We started calling three different people.”

One staffer finally called him back and told him officials were returning Friday to administer 48 more tests. Princess Cruises said in a statement that additional tests might be required by health officials.

“I think people on the ship are thinking that if tests are negative, they’ll be off,” McClelland said. “But they haven’t tested all of us that were on the past cruise.”

Despite his frustration, he praised the staffers, who, wearing masks and gloves, have been bringing meals and fresh linens and fresh towels to his door.

That was little comfort to Lisa Egan of Colorado, whose 90-year-old father was stuck on the Grand Princess. “I’m a little frustrated at not having any information,” she said.

Egan also questioned the decision to keep the ship at sea instead of transferring passengers to quarantine on land. Last month, passengers on another Princess Cruises ship, the Diamond Princess, were quarantined aboard the ship in the port of Yokohama, Japan, because of a coronavirus outbreak. The virus eventually spread to 700 people on the ship, and seven died.

Egan said her father told her that while evening entertainment had been canceled and passengers were not allowed to serve themselves at the buffet, until Thursday, passengers had still been allowed to wander the ship and congregate freely.

But in a message over the public-address system on Thursday, guests were told they needed to stay in their staterooms “for the remainder of the cruise,” in accordance with CDC recommendations. That update about the developments aboard the ship came via a YouTube channel featuring two women who have been live-streaming portions of their vacation.

In Washington, public officials insisted that they are working to avoid a repeat of the situation on the Diamond Princess. Public health experts have criticized both the cruise line and the government’s handling of that episode.

At a hearing on Capitol Hill about the federal response to the novel coronavirus, Sen. Maggie Hassan (D-N.H.) asked why the passengers on the Grand Princess were being held offshore in a closed environment, where the virus could spread.

“We determined, I thought, that it wasn’t a good idea if there was a positive result on a cruise ship to keep everybody on that cruise ship together,” Hassan told acting deputy secretary of homeland security Ken Cuccinelli, who testified at the hearing. “Now we’re hearing that there is a cruise ship off California, and yet we don’t seem to have a protocol to get those folks off the ship, into quarantine in a way that would minimize the spread of infection.”

Cuccinelli defended the decision, saying there is not enough capacity on land to quarantine large numbers of passengers.

Cuccinelli said that if the Diamond Princess quarantine had been implemented better, the virus would not have spread as widely as it did on the ship. “That was not a successful quarantine situation,” he said.

Authorities were able to take four people suspected of having the coronavirus off a cruise ship near the coast of New Jersey last month “because it was four people,” Cuccinelli said. “If you start putting zeros on that number [of people] with heavy suspicion they’re positive, you could overwhelm local health-care capacity.”

Robert Kadlec, the assistant secretary for preparedness and response at the Department of Health and Human Services, who also testified at the hearing, echoed Cuccinelli’s assertion about a lack of capacity to quarantine coronavirus cases ashore and suggested that Congress “consider” creating more capacity for future epidemics.

Late Wednesday, Newsom said state officials would work closely with the CDC and Coast Guard on establishing protocols for the Grand Princess’s return.

He added that it was not clear where the ship would end up. “The question is, where do they arrive?” Newsom told reporters. “There may be new protocols and procedures that send the ship to another location.”

The San Francisco mayor’s office said Thursday that once testing has been done, federal and state officials will decide where the ship docks.

That still leaves the issue of passengers who were on the ship during its voyage last month alongside a man who later died in Placer County and two others who tested positive for the virus.

Judy and Mark Cadiz stepped off the Grand Princess on Feb. 21 after a trip from San Francisco to Mexico. Six days ago, Judy Cadiz said in an interview, her husband, 65, fell ill with a cough. She had milder symptoms, she said.

The Cadizes subsequently traveled all around California, she said. Judy Cadiz now worries that she might have unwittingly exposed numerous people to the pathogen, including elderly members of the Lodi Moose Lodge, where she keeps the books.

“I would feel really bad if I was exposed and spread it,” she said.

Cadiz said she is upset that Princess Cruises did not notify passengers that someone from their cruise had become severely ill with covid-19 symptoms. “I wouldn’t have gone anywhere,” she said.

She said she called her doctor, who referred her to San Joaquin County Public Health Services, which told the couple Thursday afternoon to stay where they are. She said she doesn’t know when or if they’ll be tested.

As the troubled cruise ship remained isolated off the Pacific coast Thursday, the coronavirus continued its spread around the nation — and the world.

Nevada and Maryland confirmed their first cases of covid-19, bringing the number of states with coronavirus patients to 19. The death toll in Washington state increased to 11, as health officials announced 20 new confirmed cases in King County, home to a severe outbreak at a nursing facility.

The number of confirmed cases in New York doubled to 22, Gov. Andrew M. Cuomo (D) told reporters Thursday afternoon.

The Dow Jones industrial average fell 970 points Thursday as the economic outlook for the coronavirus outbreak continued to worsen. The 3.6 percent skid canceled most of Wednesday’s rally and was in line with the punishing sell-offs that have dominated trading for weeks as the outbreak threatens economic growth.

Meanwhile, the Senate on Thursday voted nearly unanimously to approve emergency spending to combat the coronavirus outbreak, sending the measure to the White House for the president’s signature.

The unusually swift, bipartisan action by both chambers of Congress underscored the pressure lawmakers are feeling to respond after more than 150 confirmed cases around the country have led to canceled travel plans, closed schools and businesses, and heightened fears about a U.S. recession.

But many questions remain about just how prepared the country is for an expanded outbreak.

Vice President Pence, who on Tuesday said that any American with a doctor’s orders could get tested for the coronavirus, acknowledged Thursday that “we don’t have enough tests today to meet what we anticipate will be the demand going forward.”

Health and Human Services Secretary Alex Azar told lawmakers Thursday that the government will have shipped enough tests by the end of the week for 75,000 people to be tested. They will be distributed at more than 70 public health laboratories around the country, he said.

Earlier in the week, the Trump administration said it could have 1 million tests ready by the end of the week .

In Washington state, home of most of the U.S. deaths related to the outbreak, health officials scrambled to get more specialized masks for front-line clinicians.

State authorities sent an urgent request for 233,000 respirators and 200,000 surgical masks to be released from the federal government’s Strategic National Stockpile. Within 24 hours, Washington state’s liaison to the federal government, Casey Katims, was told his state would get assistance — but it would be less than half the quantity requested. After lawmakers criticized the shortages in recent days, a top federal health official said Thursday that Washington state would shortly receive an additional shipment of its requested supplies, which includes masks, gloves, eye protection and surgical gowns.

Globally, the virus has infected nearly 95,000 people and caused 3,200 deaths, and its reach shows little evidence of subsiding.

In New Delhi on Thursday, the government ordered the closure of all primary schools up to fifth grade through March 31. In the West Bank, the Church of the Nativity in Bethlehem said it would close to visitors for at least two weeks.

In Rome, Italy’s national bishops organization ordered a halt to Masses for a week in the northern regions of the country that are at the center of a mounting coronavirus outbreak. The bishops’ decision follows a government decree a day earlier that called for the suspension of most large group activities and the closure of all schools until mid-March.

Iran launched a national mobilization campaign to track and slow the spread of the coronavirus, including closing schools for the next two weeks, as the health ministry announced 591 new cases and 15 deaths in the past 24 hours.

Julie Tate, Abigail Hauslohner, Max Bearak, Ben Guarino, Steve Hendrix, Niha Masih, Hazem Balousha, Chico Harlan, Miriam Berger, Hannah Knowles, Taylor Telford, Thomas Heath, Erica Werner, Lena H. Sun and Amy Goldstein contributed to this report.