A Canadian whale-watching tour boat with 27 passengers on board sank off the coast of British Columbia on Sunday, killing at least four people, rescue officials said.A military rescue helicopter and plane were sent to the waters off the coast of Tofino after the vessel sent a distress signal around 5 p.m. local time, according to the Joint Rescue Coordination Centre (JRCC). Several other coast guard vessels were involved in the search."There were four people recovered without vital signs and the search continues for people still unaccounted for," the spokesman said."It's dark here now and obviously the priority is getting the people off the water safely."The JRCC said there were "fatalities and survivors." The Canadian Broadcasting Corporation, citing BC Ambulance, said four people were taken to hospital and five were being treated after being pulled from the water.