Bomb threats were reported at multiple airports across Canada, but the agency managing air traffic control said service had started to resume at as the police investigate.

Passengers across Canada faced long delays Thursday after bomb threats were received by air traffic control towers at some of the country's busiest areas. Authorities say threats were received at airports in Ottawa,

Nav Canada said the early morning threats affected airports in Ottawa, Montreal, Edmonton, Winnipeg, Calgary and Vancouver. Airports are returning to normal operations after Canada’s air traffic control service said YVR and some other airports received bomb threats early Thursday morning.