Officials are "urgently" checking with Canadian authorities whether any Britons are among 27 people on board a whale-watching boat which sank, killing at least five people.
The boat operated by Jamie's Whaling Station, a local tour company, got into difficulty off the coast of British Columbia on Sunday afternoon local time.
A major search and rescue operation was launched, with the boat partly submerged eight nautical miles from Tofino, on Vancouver Island, according to reports.
A spokesman for the FO said: "Following the incident in Tofino on October 25, we are urgently seeking information from the local authorities and stand ready to provide consular support to any British nationals involved."
Lt Commander Desmond James of the Joint Rescue Co-ordination Centre said the military agency's search had concluded with five people dead, 21 rescued and one person missing.
It was a clear and sunny day when the 20-metre Leviathan II, operated by Jamie's Whaling Station, made a mayday call late on Sunday afternoon, local time, in the tourist community which is a popular destination for whale watchers on the country's west coast.
John Forde, who runs The Whale Centre, another whale-watching operation, said he did not know how the boat could have 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," he said.
Jamie's Whaling Station was one of the first of its kind off Vancouver Island and had been around for many years, Mr Forde said.