A spokesman for the Transportation Safety Board, Canada's transportation regulator, said that a team was headed to the airport to investigate.
Pearson Airport said on Twitter that fire and emergency crews had responded to an "incident involving two aircraft" at its Terminal 3, and that passengers had been evacuated.
WestJet Flight 2425 has just arrived from the Mexican resort of Cancun with 168 passengers and six crew on board, and was waiting to proceed to the gate when a Sunwing aircraft backed into it. There were no passengers on the China Southern plane, Marsico said.
Toronto Pearson said that one member of the Fire and Emergency Service was taken to hospital and treated for injuries sustained from the incident. After a couple of seconds the entire thing ignited and it was chaos inside the plane.
WestJet passenger Gustavo Lobo said he and other passengers heard a crunch when the Sunwing jet collided with their aircraft.
He said the flight from Mexico had landed early, requiring the aircraft to wait on the ground before passengers could disembark.
He says he was in a seat opposite the part of the plane that was struck, and he wasn't able to hear instructions from crewmembers or the pilot over the commotion.
"I started crying because I realised what happened", she said.
She only realised how serious the situation had been once she was out of the plane.
Fire trucks and ambulances descended on the tarmac when a small fire on the Sunwing aircraft began, said Beverly MacDonald, a spokeswoman with the Greater Toronto Airports Authority.