MONTREAL (AFP) - Cold weather halted all flights at the Toronto international airport - Canada's busiest commercial air hub - Tuesday, after temperatures plunged overnight, stranding thousands of passengers.

"Extreme cold causing equipment freezing and safety issues for employees," the airport said in a Twitter message.

Hundreds of flights were cancelled. Incoming aircraft were diverted, while a backlog of jetliners waiting to take off jammed the tarmac and fuming passengers huddled at departing gates, flanked by police called in to provide extra security.

According to Canada's weather office, temperatures fell to -40 degrees Celsius (-40 Fahrenheit) overnight, from above freezing.

Flights were to resume at 9 am (11 pm Singapore time) but the airport only began clearing aircrafts for take off or landing an hour later.