UPDATE - Oct. 26, 2015: British Foreign Secretary Philip Hammond has confirmed five tourists British died in the accident.
Of the 27 people aboard the boat when it capsized, 21 people were rescued and one person was still missing, said a spokesman with the Joint Rescue Co-ordination Centre.
Officials ended the search late Sunday night and turned the incident over to the RCMP.
TOFINO, B.C. - Several people are dead after a weekend whale-watching expedition on British Columbia's west coast ended with a vessel capsizing, sending dozens of people into the ocean water.
Joe Martin, a member of the Tal-o-qui-aht First Nation, was near the dock when the rescue boats began returning to the tourism community of Tofino.
"I did see a boat come in with three bodies on board and then another one arrived and there were two."
Martin said two people were brought in on a Zodiac, where workers tried to resuscitate them but eventually covered them with blankets.
He said his brother and nephew were out halibut fishing when they saw the overturned boat and tried to help. Instead, the men pulled in three bodies, he said.
The ship was on the far side of Vargas Island in Clayoquot Sound, an area that Martin said could get really rough.
"It wasn't even blowing hard (Sunday). This is the largest boat in Tofino and I was really surprised that it went down."
Various sources including the area's newly elected MP identified the boat as the Leviathan II, a 20-metre vessel belonging to the local whale watching outfit Jamie's Whaling Station.
An employee of the company who answered the phone would not take any questions.
"I hope you can understand that all of our focus and energy is on the passengers and crew right now and we don't have any information and we will be releasing it when the time is appropriate,'' she told The Canadian Press.
Lt.-Cmdr. Desmond Craig, a spokesman with the Joint Rescue Co-ordination Centre, said the boat made a mayday call late Sunday afternoon.
Coast Guard vessels and search and rescue aircraft were searching for people on the boat who were still unaccounted for, though Craig said he could not say how many people were still missing.
The Leviathan had 24 passengers and three crew members on board at the time of the incident, said emergency officials.
Brandon Hilbert from Tofino Water Taxi said local companies all pitched in to help with the rescue effort.
Some of the first boats to arrive on scene were from the nearby Ahousaht First Nation, said aboriginal Coun. Tom Campbell.
He was on the Tofino waterfront and watched as rescue personnel brought several of the survivors ashore.
"Their looks tell the whole story,'' he said by telephone from Tofino. "You can't describe looks on people that are lost. They look totally lost — shocked and lost.''
Campbell, who wasn't on the water, said his cousin pulled at least eight people from the water into a boat on Sunday afternoon.
He said the First Nation held an evening meeting to discuss launching further rescue operations in the morning, adding that he would contribute his two boats to the search.
Meanwhile, community members in Tofino rallied to offer help, bringing food, blankets and clothing to survivors and rescuers alike.
The mayor of Tofino described the mood in the town as tense but commended locals for their contributions.
"Everybody's heart is just breaking for what's going on here and wanting to be as helpful as possible," said Josie Osborne in a telephone interview late Sunday.
John Forde, who runs The Whale Centre, another whale-watching operation in the community, responded to the call for help and was told early Sunday evening that rescuers were still looking for four or five missing people.
"It's a pretty sad situation when you're doing a grid pattern to an area hoping to see something,'' he said, adding that it didn't look hopeful as the time dragged on without finding survivors.
He said he had no idea what might have happened.
"Over the course of a season and years we take out thousands and thousands of people on these trips in conditions similar today. I have no idea what the issue was or what actually happened.
Forde said Jamie's Whaling Station was one of the first such whale-watching operations on the west coast of Vancouver Island and had been around for many years.
This isn't the first fatal incident on the company's record. In 1998, one of their smaller vessels capsized during a sightseeing excursion, sending all four people on board into the water. The operator and one of the passengers died.
The Transportation Safety Board confirmed it was investigating Sunday's incident.