Travellers were left scrambling after a fire at Toronto's Pearson International Airport.

Smoke could be seen filling the halls of terminal one on Sunday night, forcing hundreds of people to be evacuated. All flights to the U.S. were cancelled, and several international flights were delayed until Monday.

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The aftermath of the fire/smoke for Internationals checkpoint at #yyz handled and taken care of in under an hour

A post shared by Saq (@saq_saiyed) on Mar 17, 2019 at 10:06pm PDT

It's unclear exactly how the fire started, though it broke out at around 6:30 p.m. and was quickly extinguished.

Toronto #pearson #yyz has closed international departures for some sort of fire inside the airport..

It's always something in this place. pic.twitter.com/eE9a5kg0rC

— jamesagnew (@jamesagnew) March 17, 2019

Luckily, no serious injuries were reported, though paramedics treated a few people for "smoke-related injuries," and one person was taken to hospital for further treatment.

Ummm @TorontoPearson #pearsonairport is on fire... pic.twitter.com/6t58zgveM4

— Kendall Wilson (@kendallnwilson) March 17, 2019

The airline tweeted just after 3 a.m. that terminals one and three were back to regular operations, and flights to the U.S. were expected to resume Monday morning.

Both Terminals 1 and 3 are operating normally, with the exception of Terminal 1 departures to the United States, where some delays may be experienced. Please check your flight status with your airline before leaving for the airport. https://t.co/VPZ071V8vB

— Toronto Pearson (@TorontoPearson) March 18, 2019

Airport authorities said they're expecting a busy Monday as they try to clear a backlog of flights.