Five British nationals died when the whale-watching boat Leviathan II sank off the coast of Tofino, B.C., officials say.

British Foreign Secretary Philip Hammond confirmed the victims’ nationalities in a statement released Monday.

Investigators are trying to determine what caused the vessel to capsize Sunday, killing five of the 27 passengers and crew who were tossed into the frigid water.

All four hospitalized passengers were listed in stable condition Monday.

Rescuers pulled 21 survivors out of the water and all were taken to hospital. Seventeen people were released, while three remain in different hospitals on Vancouver Island. One person was taken to Vancouver General Hospital.

B.C.’s Joint Rescue Coordination Centre said five bodies were also recovered and another person remains missing. The RCMP are continuing their search for the missing passenger, along with the Coast Guard.

The Leviathan II cruiser vessel made a mayday call shortly after 4 p.m. local time, prompting nearby residents and search-and-rescue workers to rush to the scene to help.

The JRCC in Victoria dispatched a Royal Canadian Air Force Cormorant helicopter and an RCAF Buffalo aircraft, while the Canadian Coast Guard sent out four fast-rescue craft.

Lt. Paul Trenholm of the Joint Rescue Co-Ordination Centre said the quick response from nearby boats saved lives.

“Without the collaborative effort of the people that were living nearby, rendering assistance, this could have been much worse,” he told CTV News Channel Monday.

It remains unclear what caused the 20-metre vessel to capsize. The boat was on the far side of Vargas Island in Clayoquot Sound, an area were the waters can become rough. But local residents say while it had been raining lightly earlier in the day, the weather was mostly clear when the capsizing happened.

CTV Vancouver Island’s Gord Kurbis said the vessel went down in an area called Plover Reefs, which is popular with whale-watching vessels because there’s a lot of marine life there.

“One of the theories is the vessel struck one of the rocks near the area and that’s when people were tossed in the water,” he said.

The Leviathan II was operated by Jamie’s Whaling Station, which Kurbis said was one of the larger whale-watching operations in the area. But he said it’s a small tight-knit community in Tofino and the accident will affect the whole tourism industry.

“Even though it was that one company that was affected, all of them are feeling the pain of what’s gone on here,” he said.

Jamie’s Whaling Station released a statement late Sunday to say they will be co-operating with the Transportation Safety Board of Canada investigators, to determine what happened.

“It has been a tragic day,” their statement read. “Our entire team is heartbroken over this incident and our hearts go out to the families, friends and loved ones of everyone involved.”

They also thanked the first responders, rescue personnel, and the residents from Tofino and the local First Nations communities who assisted with the rescue.

Chris McLellan, who lives nearby, told CTV News Channel that other whale-watching tour boats as well as residents from the nearby Ahousaht First Nation were the first to respond to the mayday call.

“Everyone just converged when they heard on the radio what was happening,” said McLellan.

Sheila Simpson was strolling on the Tofino dock with her husband when rescue boats roared up carrying people from the whale-watching vessel. She told The Canadian Press she managed to comfort some of the survivors as they stood on the dock awaiting transport to hospital.

“They were in absolute shock,” she said. “You could see it in their eyes. ‘This didn’t happen. We came on a holiday’.”

Alec Dick, the emergency coordinator for the Ahousaht First Nation, told CTV News Vancouver that he was surprised to hear of a 20-metre vessel capsizing, saying that in all his years of responding to marine emergencies, he had never heard of a boat that big being flipped over.

A similar tragedy with a whale watching boat happened nearly two decades ago in the Tofino area.

Tofino Mayor Josie Osborne told CTV News Channel Monday that Transportation Safety Board investigators have arrived in town to determine how the boat capsized.

She said the response from the community has been “nothing short of phenomenal,” with other whale-watching tour operators and businesses in the area rallying together.

Osborne said the local tourism industry is well-regulated and she’s “confident” that the boats operated by Jamie’s Whaling Station have been regularly inspected.

Right now, “the community of Tofino is very much focused on the passengers and survivors,” Osborne said, adding that counselling services will be offered to those affected.

A community gathering is being planned for Monday evening, she said.

Condolences for the victims and their families have been pouring in from across the country, including a statement from prime minister-designate Justin Trudeau, who said he was “shocked and saddened” to hear about the tragedy.

“We thank all those, including our search and rescue officials, who responded swiftly with courage and professionalism,” he said.

“I know firsthand of this coastal area’s natural beauty and the many people who visit here from all around the world. My thoughts and prayers are with the passengers, the crew, and their families at this most difficult time. We will continue to offer them support in the days ahead.”