An Australian man is missing feared dead and five British nationals have died after a whale watching boat sank off Vancouver Island.
AAP has been told by the family of a Sydney man, 27, that he was on the MV Leviathan II with his girlfriend and her family when it went down.
Her father was one of five British citizens confirmed dead.
The parents of the missing Sydney man were desperately trying to arrange an emergency passport on Tuesday to travel to Canada.
The Department of Foreign Affairs said it was providing consular assistance.
The ages of the four men and one woman, two of whom were Canadian residents, ranged from 18 to 76.
The Royal Canadian Mounted Police have sent an underwater recovery team to search for the missing man, with assistance from the Coast Guard and local search and rescue personnel.
"We still remain hopeful, but we have to assume the worst," said RCMP Corporal Janelle Shoihet.
The others onboard were rescued, some by members of the local indigenous community who rushed to help, but the cause of the sinking is not known.
The 20-metre boat sent up a flare late on Sunday afternoon on a calm, clear and sunny day 12km off Tofino, a resort town on the western edge of Canada's Vancouver Island.
The boat, undertaking one of the last tours of the whale-watching season, capsized in waters less than 10 metres deep, raising suggestions it may have hit rocks.
Jamie Bray, the owner of the operating company, is cooperating with investigators.
"Traumatised would be an appropriate word. Disbelief," Mr Bray told reporters of the capsizing.
The boat - which had 24 passengers and three crew - had visited the area almost every day for the past 20 years with an unblemished safety record.
"This is something just totally out of the blue," Mr Bray said.
He said life jackets are not worn on ships that have enclosed compartments in the event of a sinking because of the difficulty they cause in trying to exit a vessel.
"On larger vessels we're not required to have the passengers wear the life jackets. On smaller open boats they are," he said.
British Foreign Secretary Philip Hammond confirmed in a statement that the five killed were UK nationals.
"My thoughts are with the family and friends of all those affected by this terrible accident," Mr Hammond said.
Marc-Andre Poisson, from Canada's Transportation Safety Board, said it was too early to say what were the causes and contributing factors.
The company has been involved in two previous incidents.
In 1998 one of its vessels capsized during an excursion, sending all four people on board into the water, resulting in the deaths of the operator and a passenger.
In 1996, a boat operator fell asleep and ran into rocks. The boat was destroyed and the operator was seriously injured but there were no passengers on board.
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