OTTAWA — The five people known to have died when a whale-watching boat sank off the coast of British Columbia on Sunday were British, according to Philip Hammond, the British foreign secretary. Twenty-one people were rescued from the sinking, and one person remained missing on Monday.

“My thoughts are with the family and friends of all those affected by this terrible accident,” Mr. Hammond said in a statement on Monday that did not identify the victims or say where they lived.

Lt. Paul Trenholm of the Royal Canadian Navy, speaking for a rescue center operated by the military and the coast guard, said the boat sank Sunday afternoon about eight nautical miles from Tofino, a popular vacation spot on the west coast of Vancouver Island.

After its crew sent up flares, the boat was quickly located by four coast guard boats and a large number of private vessels, many from a coastal aboriginal reserve. The boat was found partly submerged, with its bow rising above the water.