Media playback is unsupported on your device Media caption Marine investigator: "It is much too early to say what the causes and contributing factors of this accident might be"

A whale-watching boat which sank off the coast of Canada, killing five Britons, had no opportunity to send a Mayday call, its operator has said.

More of the 27 people on board Leviathan II could have died had it not been for the "amazing response" from locals around Tofino, officials said.

An Australian is missing after the incident near Vancouver Island, the Australian government said.

Canadian government investigators have now arrived at the scene.

Media playback is unsupported on your device Media caption Amateur video shows the stricken whale-watching boat in the sea

British Columbia coroner's office said the victims, four men and one woman, ranged in age from 18 to 76.

The cause of the accident remains unknown but sea conditions at the time of the incident were said to be calm.

'Flipped'

Canada's Transportation Safety Board says it could take many months to establish what happened.

One eyewitness Alec Dick, from nearby Ahousaht First Nation, told Canada's Global News network the boat had been flipped "completely" by a wave.

Corene Inouye, director of operations at Jamie's Whaling Station and Adventure Centre, the company that owns the boat, said: "It appears the incident happened so quickly that the crew didn't have an opportunity to send out a Mayday."

She added the skipper of the ship has more than 20 years' whale-watching experience and had completed 18 years with the company.

Company owner Jamie Bray said passengers on the boat were not required to wear life jackets as it has enclosed compartments, which would be difficult to exit in the event of a sinking.

Image copyright Reuters Image caption Officials praised the "amazing response" of local people

Image copyright Reuters Image caption Rescue boats have continued to search for the missing passenger

Image copyright Reuters Image caption Corene Inouye of Jamie's Whaling Station and Adventure Centres spoke to reporters on Monday

At the scene

BBC correspondent James Cook at Tofino, Vancouver Island

Why the Leviathan II went down is a mystery which investigators say they may not solve any time soon.

As well as interviewing survivors and other witnesses, the Transportation Safety Board will be looking into conditions on Sunday, as well as scouring the wreckage of the whale-watching boat for clues, and examining its maintenance history.

The vessel, still submerged, has been towed from the scene to a nearby island so the work can begin.

The weather at the time of the accident was reportedly benign but sailors familiar with these waters say powerful currents, rogue waves and rocks are all potential hazards, even when the conditions appear to be favourable.

A lengthy investigation will be difficult for some to bear. Those touched by this tragedy may well want to know as soon as possible how this could have happened to the same tour operator for a second time.

'Amazing response'

Greg Louie, chief councillor of the Ahousaht First Nation Elected Council, told the BBC Radio 4 Today programme that had the local community not responded to the accident so quickly "possibly everyone" could have drowned or died of hypothermia.

The incident could have been "a lot worse", Lt Cmdr Desmond James of the Canadian Joint Rescue Co-ordination Centre in British Columbia said.

He added that 21 people would not have been rescued were it not for the "amazing response" by the local community.

Three of the victims were tourists on holiday from the UK, while two were UK nationals living in Canada - one woman from British Columbia and a man from Ontario.

Australian Associated Press reported the missing 27-year-old Sydney man was on the boat with his girlfriend and her family when it sank.

His girlfriend's father was among the five Britons confirmed dead, the news agency said.

Another whale-watching boat operated by Jamie's Whaling Station and Adventure Centre capsized in 1998, killing two people, including the boat operator and a tourist from Germany.

The six-metre vessel was on a three-hour trip in the area of Plover Reef when it was hit by a large swell, throwing four people into the water.

Image copyright Reuters

Whale watching off British Columbia

Tofino is a popular surfing and whale-watching resort near the Clayoquot area

Whale-watching season in Tofino begins in March and ends in late October

The area's rugged coastline and national parks attract tens of thousands of tourists every year

Canada has over 200,000km (124,000 miles) of coastline, meaning it is one of the best locations for whale watching

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