At least three people died after a whale watching boat with 27 people on board sank off Vancouver Island and a rescue mission remained active late Sunday, Canadian authorities said.

The vessel made a mayday call late Sunday afternoon on what was a clear and sunny day in the tourist community that is a popular destination for whale watchers on Canada's West Coast, the Joint Rescue Coordination Centre said.

Lt.-Cmdr Desmond Craig, a spokesman for the rescue agency staffed by Canadian military and Coast Guard personnel, said four people were pulled from the water without vital signs, but he couldn't confirm how many had died. Craig could not immediately say how many people on the boat remained unaccounted for.

Lt. Commander Desmond James of the center said the boat was partially submerged 8 nautical miles (12 nautical kilometers) west of Tofino.

Valerie Wilson, a spokeswoman for the Island Health hospital agency, said eight people had been admitted to Tofino General Hospital. She said seven were stable and one was in serious condition, but stable.

"Everybody's heart is just breaking for what's going on here and wanting to be as helpful as possible," Craig said.

Coast Guard vessels and search and rescue aircraft were searching for people on the boat who were missing. The helicopter and aircraft being used in the waters off of Tofino had equipment to search in the darkness.

Boats from the nearby Ahoushat First Nation arrived first on the scene, said aboriginal Councilor Tom Campbell. He was on the waterfront and watched as rescue personnel brought several survivors ashore.

"Their looks tell the whole story," he said by phone 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 runs The Whale Centre, another whale watching operation, responded to the call for help and was told the search was 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 time dragged on without finding more survivors.

The ship that went down was the 20-meter Leviathan II, operated by Jamie's Whaling Station, Forde said. He said he had no idea how it could've sunk.

"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.

Forde said Jamie's Whaling Station was one of the first of its kind off Vancouver Island and had been around for many years.

It wasn't the first fatality on the whale watching company's record. In 1998 one of its vessels capsized during an excursion, sending all four people on board into the water. The operator and a passenger died.

Asked how many were dead off Tofino, British Columbia Coroner spokeswoman Barb McLintock said earlier Sunday in an email: "Multiple but we don't yet have a firm number. Still a very fluid situation so we really are not sure yet."

Jenn Hamilton, a spokeswoman for British Columbia Emergency Health Services, said five ambulances were dispatched and several off-duty paramedics went to the dock to help.

Tofino Mayor Josie Osborne tweeted "thoughts & prayers are with passengers, crew, emergency responders & their families."

The Transportation Safety Board confirmed it was investigating Sunday's incident.

Brandon Hilbert from Tofino Water Taxi said local companies all pitched in to help in the rescue effort.

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Associated Press Writer Rob Gillies contributed to this report from Toronto.