Rescue personnel mounting a search for victims of a capsized whale watching boat park on a wharf in Tofino, British Columbia October 25, 2015. [Photo/Agencies]

DUNCAN, British Columbia - A Canadian whale-watching tour boat with 27 passengers on board sank off the coast of British Columbia on Sunday, killing at least four people, rescue officials said.

A Canadian military rescue helicopter and plane were sent to the waters off the coast of Tofino after the vessel sent a distress signal around 5 pm local time, according to a spokesman for the Joint Rescue Coordination Centre (JRCC). Several other coast guard vessels were involved in the search.

"There were four people recovered without vital signs and the search continues for people still unaccounted for," the spokesman said.

"It's dark here now and obviously the priority is getting the people off the water safely."

Earlier, the JRCC said there were "fatalities and survivors." The Canadian Broadcasting Corporation, citing BC Ambulance, said four people were taken to hospital and five were being treated after being pulled from the water.

The manager of the Shelter Restaurant in Tofino said fishermen and fishing charter companies had joined the rescue effort, with about 15-20 boats leaving the tourist town.

"Practically anyone who can go will go," said Matthew, who did not give his last name. "People here get together to help when things like this happen."

The area is popular for whale-watching.

"All our attention now is on our passengers and crew so we'll be providing information as soon as the time is appropriate," said a staff member with Jamie's Whaling Station and Adventure Centres, which operated the vessel.

The Transportation Safety Board of Canada said it would send a team to Tofino to investigate.