Emergency officials across the region Thursday were preparing staff, stocking up on equipment and increasing the number of rescue vehicles in response to the deadly heat wave that has seized the area and is not expected to subside until Sunday.

The suffocating temperatures, which hovered over the central part of the nation before moving east, had claimed about two dozen lives before reaching the Washington region. Authorities had reported no heat-related fatalities here, but excessive heat warnings were in effect, and heat indexes were expected to reach dangerous levels through Saturday — near, if not above, 110 degrees.

In the District, fire and EMS spokesman Pete Piringer said Thursday night that he expected the department would transport more than 300 people to area hospitals by midnight, with the “vast majority” suffering from such heat-related afflictions as heatstroke, exhaustion and dehydration.

It was the start of a run of dangerous weather that would divide the area into two groups: the merely uncomfortable and the truly vulnerable.

Before Elnorah Jordan left her house in Anacostia, she made sure she had her ID. She suffers from asthma, HIV and high blood pressure and was worried about the potential consequences of a 20-minute walk to a health-care center. What if she fainted and a stranger found her?

“I don’t want to be a Jane Doe,” said Jordan, 37.

Throughout the region, emergency officials reported an increase in heat-related illnesses. In Prince George’s County, emergency medical services officials said they had seen an increase of 15 to 20 percent in medical calls, including reports of fainting, dizziness and headaches. In Arlington County, rescue crews increased their fleet of ambulances from seven to nine to handle the calls.

Mental health centers also prepared to handle patients, some with medications that can have different effects in extreme temperatures, said Millicent West, director of the D.C. Emergency Management Agency.

At Children’s National Medical Center, Stephen Teach, associate chief of emergency medicine, said the staff had discussed what to expect because of the extreme temperatures and made sure it had plenty of equipment on hand, including fans and ice. Infants, he said, are the most vulnerable to overheating, and older children can face the risk of heat exhaustion or heatstroke.

“The best way to manage heat-related illness is to prevent it,” Teach said. The heat wave also highlights what doctors cannot prevent or treat: Patients might leave the hospital only to return to a home where there is no air conditioning or electricity.

That’s where Health Leads, a program run out of Children’s, picks up. On Thursday, there were double the number of volunteers on hand: four young women in matching blue shirts, one still in high school and the rest in college, sat waiting to greet families that might walk in. On Wednesday, a woman and her mother came in with an infant and a 6-year-old, wanting only to sit in the office because they had no air conditioning at home.

“In this heat, it’s not just about discomfort,’” said Latoya White, executive director of the program. For many people, she said, it’s about “survival."

If there was any consolation to be found, it might have been in the region’s power lines, which were standing up fairly well to the challenge. At 9 p.m., fewer than 5,000 customers in the Washington region were without electricity. Montgomery County had the most outages, at 2,655, and 1,100 were reported in Prince George’s County.

But for most people across the region, the heat still amounted to sweat-drenched backs and adjusted routines. Men who would normally wear ties went without. Long-haired women who usually wear their hair down didn’t dare.

Jerry Rafats, 71, a retired agricultural librarian, would usually get up by 7 a.m. but said he stayed in bed until 10 watching a bad Jenny McCarthy and Carmen Electra romantic comedy on Net­flix. He then trudged out from the air conditioning to try to bring some relief to his heat-stressed tomato plants before resuming his usual schedule with a trip to the Rockville Senior Center for the treadmill and some light weights.

The plan for Friday, he said: “Just go to my yoga class and probably drink a lot of ice-cold lemonade and watch movies.”

The Falls Road Golf Course in Potomac saw a drop in visitors: about 190 stalwarts hit the greens on Thursday, down from a typical 300.

Lou Eighmey, 72, played 18 holes with his wife, Kathy, 67. They’ve been married 43 years and try to play at least two rounds a week. Eighmey said they took advantage of iced-down towels handed out to golfers on the course.

“It’s hotter than all blazes out there,” he said after carding a 94.

For many, staying indoors Thursday was not an option. Work needed to be done, and at road-repair sites, sweat-drenched crews doused themselves with ice water.

On S Street in Northwest Washington, Hug Stanfield, 25, stood in a sliver of shade on the south side of the street, grateful for a brief respite. He was part of an excavation crew, and, for the moment, he had the relatively easy job of directing traffic. Most of the time, he’s in the pit, digging, with no shade.

“The working conditions are unbelievable,” Stanfield said. “But we have to do what we have to do to take care of our families.”

When he got home, he said, he planned to take a shower, have a cool drink and lie down.

The next day, he’d heard, was supposed to be hotter.

Staff writers Sarah Khan, Victor Zapana, Ovetta Wiggins, Ruben Castaneda, Ashley Halsey III, Donna St. George, Michael Laris, Dan Morse, June Q. Wu and Keith Alexander contributed to this report.