A whale-watching boat has sunk off the coast of British Columbia in western Canada, leaving at least five people dead, the BBC reports.

The boat carrying 27 people sank near Tofino on Vancouver Island, the coastguard said. Sea conditions at the time were reported to be calm.

Emergency officials said 21 people had been rescued and one other person was still missing.

The nationalities of the victims are not yet known.

The boat, Leviathan II, made a mayday call late on Sunday afternoon, the Joint Rescue Co-ordination Centre said.