Image caption Clockwise from left: David Thomas and son Stephen, Katie Taylor, Jack Slater and Nigel Hooker died in the incident

Most passengers on a whale-watching boat which sank off Canada were standing on the vessel's left side when a wave hit it from the right, affecting its stability, investigators say.

It comes as more details emerged about the five Britons who died when Leviathan II sank near Tofino on Sunday. An Australian man is missing.

Canadian investigators said the vessel tilted and then capsized.

Passengers were not required to wear life jackets, but they were available.

The Transportation Safety Board of Canada (TSB) said an examination of the vessel would begin on Wednesday to "understand its condition at the time of the accident".

Tributes have been paid to David Thomas, 50, and his son Stephen, 17, from Swindon, who were among the dead. Stephen's mother Julie was rescued.

Nigel Hooker, 63, from Southampton, Salford-born Jack Slater, 76, who had lived in Canada for many years, and Katie Taylor, 29, who was living in Whistler, British Columbia, also died.

Image copyright AP Image caption The boat sank off British Columbia

Marc Andre Poisson, director of marine investigations for the TSB, told a news conference the position of most people on one side of the boat would have "raised the centre of gravity" and affected the boat's stability.

"We also know that the sea conditions were such that a wave approached from the starboard quarter, that's the right of the vessel," he added.

"We know that the vessel broached and then capsized."

Who were the victims?

Image copyright AP Image caption Tributes at the scene

David Thomas had worked for technology giant Microsoft, which said it was "shocked and saddened" by his death.

His son Stephen was described by the Down's Syndrome Association as "a very talented young man and a gifted photographer".

Nigel Hooker had been visiting Canada from Southampton. He worked for Airbus Defence and Space as a programme assurance manager in Portsmouth. They said he was "a well respected and popular colleague, and will be greatly missed by everyone he worked with".

Jack Slater was born in Salford but had lived in Canada for more than 30 years. His daughter, Michele Slater Brown, said he was "larger than life, a charmer, handsome, entrepreneur" and a "lovely dad".

Katie Taylor was also an ex-pat, and was originally from Lichfield in Staffordshire, but lived in the ski resort of Whistler. She was described as a "vibrant, outgoing and lovely young woman" by her family.

The TSB said its examination of the vessel would review "stability information at the time of its construction, and examining any modifications that have been made since its initial construction that may have affected its stability".

The five people who died had been on the open, upper deck of the boat, but were not wearing life jackets, regional coroner Matt Brown told a news conference.

Current regulations do not require passengers to wear life jackets in that area or on that particular type of boat, he said.

The other passengers were all in an enclosed part of the boat.

Media playback is unsupported on your device Media caption Vancouver Island regional coroner Matt Brown: "This is a tragic outcome for the families, the community and the public"

Officials have said more of the 27 people on board could have died had it not been for the "amazing response" from locals around Tofino.

Bosses at Jamie's Whaling Station and Adventure Centre, which owned the boat, have said the incident happened so quickly the crew did not have chance to send a Mayday alert.

They said the skipper 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.

Another whale-watching boat operated by the same company capsized in 1998, killing two people, including the boat operator and a tourist from Germany.

Media playback is unsupported on your device Media caption Fisherman Clarence Smith: "We took 10 people off the life raft and on to our boat"

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

British Foreign Secretary Philip Hammond said his thoughts were with the family and friends of those affected by Sunday's incident.

Canadian prime minister-designate Justin Trudeau said he was "shocked and saddened" by the deaths.

Image copyright Reuters

Whale watching off British Columbia