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 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 is 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.