Rescue personnel searching for victims of a capsized whale-watching boat park on a wharf in Tofino, British Columbia on Oct. 25, 2015.  (Adam Chilton/Reuters)

A whale-watching boat sank in the cold waters off Canada’s Vancouver Island late Sunday afternoon, killing at least five of its 27 passengers and crew members.

Lt. Commander Desmond James, a spokesperson for Canada’s Joint Rescue Coordination Center, said that 21 other people have been recovered from the water. One person remains unaccounted for.

The Joint Rescue Coordination Center has called off its search and rescue operation, James said. The Royal Canadian Mounted Police will take over any search and rescue efforts for last missing passenger.

It’s not clear what led the JRCC to call off its effort. James said that “there would be an indication that there’s a reason not to continue to search” — perhaps the entire area around the scene had been searched, or the window of survivability had passed — but he’s not sure what the indicator was in this case.

According to James, the tourist vessel, the Leviathan II, sank around 5 p.m. local time and was found partially submerged about eight miles from the small town of Tofino. It’s not yet known what caused the boat to sink, though James said the weather was good when rescue workers arrived on the scene 30 minutes after the initial mayday call.

As of late Sunday night, the boat was being towed back to shore.

Barbara McLintock of the British Columbia Coroners service confirmed that five people from the boat have been declared dead. She added that there is a fear that the number might go up.

“One person remains unaccounted for, and some of the ones taken to the hospital are not in good shape,” she said. “But we’re really hoping it doesn’t.”

It is too soon to say whether the five victims died of hypothermia, drowning or some other cause, she said.

Valerie Wilson, a spokeswoman for the Island Health hospital agency, said that 18 patients were taken to Tofino General Hospital after the accident Sunday night, three of whom were then transferred to other hospitals on the island. Some of the 15 who remained in Tofino have already been discharged, and Wilson said there would continue to be discharges throughout the night. She could not say anything about the condition of the hospitalized victims, or what illnesses or injury they suffered.

The Transportation Safety Board of Canada says it will be sending a team of investigators to look into the incident.

Coast guard vessels, local whaling boats and other rescue ships swarmed to the spot where the tour boat went down, but boats from the nearby Ahousaht First Nation were the first to arrive on the scene. Ahousaht Councilor Tom Campbell watched from the waterfront as rescue boats brought survivors to shore.

“Their looks tell the whole story,” he told the AP from Tofino. “You can’t describe looks on people that are lost. They look totally lost — shocked and lost.”

Campbell said his cousin pulled at least eight people from the water into a rescue boat.

John Forde, who owns the Tofino Whale Centre and is a captain at the local fire department, was giving a tour of nearby hot springs when he heard about the capsized boat and changed course to help with the search.

He arrived to find the Leviathan II nearly submerged.

“It was quite close to the rocks and you could still see part of the vessel above water,” he told the CBC. “There was a lot of injured and hypothermic people being brought in Ahousaht water taxis, at least a dozen boats out there if not more.”

The Leviathan II was operated by Jamie’s Whaling Station, a local tour company. According to the company’s Web site, the boat is a 65-foot cruiser, and it’s described as “Tofino’s largest and most comfortable whale watching vessel.”

Jamie’s Whale Station has run tours near Tofino for more than three decades and has seen at least one other fatal incident. In 1998, a wave flipped one of the company’s inflatable whale-watching boats, killing the boat’s captain and one passenger, according to a Seattle Times article from the time. Two others were also on board when the boat capsized.

The 1998 deaths were the first known fatalities related to Tofino’s thriving whale-watching industry, the Seattle Times reported.

Tofino’s mayor, Josie Osborne, said that the mood in the small tourist town was tense. The coastal community of less than 2,000 people is popular with whale watchers, fishermen and nature lovers, but it has few resources for this kind of tragedy. McLintock of the coroner’s service said that coroners had to be sent in from elsewhere to examine the bodies of the five confirmed victims — the town is much too small to have its own.

“Everybody’s heart is just breaking for what’s going on here and wanting to be as helpful as possible,” Osborne told the AP.

Fishing guide Lance Desilets spent the evening out on the water, helping to recover debris from the accident.

“There was lots of personal belongings floating around, purses, backpacks, cameras, that sort of thing. Pretty grim,” he told the Vancouver Sun.

Two lifeboats floated nearby. No one was in them.

“I’ve been a fishing guide in Tofino for 15 years, and I’ve never seen anything like this before. It’s disturbing,” Desilets said.

Rami Touffaha, another tour boat operator in Tofino, watched the rescue operations from a nearby dock. He said it looked like all of the town’s limited rescue resources were out at the scene.

The cause of the accident is a mystery to him — the weather was beautiful on Sunday, he told the CBC, and the sun was shining.

“The waters weren’t choppy so I don’t see what could have caused the boat to sink,” Touffaha said. “But you never know in these waters unfortunately.”