The Transportation Safety Board of Canada has sent two investigators to Toronto's Pearson International Airport to assess a collision between two planes on the ground that sparked a fire and injured an airport firefighter.

The board hasn't yet commenced an investigation, but among the questions asked would be whether WestJet followed its evacuation protocols and what caused flames to break out on the Sunwing plane involved, among other things, TSB spokesperson Chris Krepski told CBC News.

So far, said Krepski, investigators have completed interviews with the flight crew and have obtained the data recorder and voice recorder from both planes.

WestJet Flight 2425, arriving from Cancun, had 168 passengers and six crew on board, and was waiting to proceed to the gate when it was hit by the Sunwing aircraft moving back from a gate Friday at 6:19 p.m. ET on the apron of Terminal 3.

The Sunwing plane caught fire and the WestJet plane had to be evacuated, with passengers forced to leave through two emergency slides. The Sunwing aircraft, a Boeing 737, was not carrying any passengers or crew and was being towed by the airline's ground handling service, Swissport.

None of the passengers were taken to hospital, but an airport firefighter was injured following the collision, BeverlyMacDonald, spokesperson for the Greater Toronto Airports Authority, confirmed on Saturday.

Peel Regional Paramedic Service says the firefighter's face was exposed to a chemical and he was taken to hospital.

Video captures smoke and fire after empty Sunwing strikes WestJet with passengers aboard. 0:23 Jay Szymanski, superintendent for Peel paramedics, said the chemical involved may have been antifreeze and the injuries are considered minor.

MacDonald said the firefighter has been treated and released and is expected to make a full recovery.

Paramedics also assessed passengers at the scene of the collision, but Szymanski said no one else was transported and it is not known how many passengers were assessed.

Collision 'still being assessed'

Krepski said Saturday that TSB investigators arrived at the airport at about 9 p.m. to interview passengers and ground, cabin and flight crew and managers in charge of ground crew.

He said the investigators are gathering information to determine if an investigation should be conducted. They were expected to examine the accident scene and aircraft involved in the collision.

Peel Regional Paramedic Service said passengers were assessed at the scene of the collision but none were transported to hospital. (CBC) "This occurrence is still being assessed," he said.

"We haven't decided one way or another whether we're investigating. At this point, we've deployed to gather more information. One of the information elements we would seek to gather would be how many ground crew were present, how many are required, what the procedures are for this type of manoeuvre."

WestJet has confirmed that its plane was a Boeing 737-800. The Sunwing aircraft, a Boeing 737, was not carrying any passengers or crew and was being towed by the airline's ground handling service, Swissport.

The Sunwing aircraft was not carrying any passengers or crew when it clipped a WestJet flight on the tarmac of Pearson International Airport. (Megan Fill) "We are aware of an incident that occurred yesterday evening at Toronto Pearson Airport where a Sunwing aircraft, under tow by Swissport, our ground handling service provider, came into contact with another aircraft," Sunwing said in a statement on Saturday.

Fire and emergency services responded. Both airlines said they are in contact with the TSB and GTAA.

WestJet said passengers who are connecting to other flights were given hotel accommodation and meal vouchers. It said it is working to get the passengers to their final destinations as soon as possible.

MacDonald said the accident site has been cleared.

She said there were delays at Pearson following the collision because planes were not allowed to enter the area where it occurred immediately afterward, but operations have resumed, although they are still affected by extreme cold weather conditions.

"Operationally, the effects of the incident have been cleared. However, due to the extreme cold weather in Toronto, there could be some delays and cancellations for Saturday," she said in an email.

Swissport 'regrets' collision

Pierre Payette, Swissport Canada Handling Inc. vice-president of operations for Toronto, said the number of Swissport employees servicing the Sunwing plane was in line with company's standard operating procedures and consistent with regulations across the airport.

"Ensuring the safety of our staff, our partners and travellers is paramount to Swissport. We regret this incident and are cooperating fully with the Transportation Safety Board of Canada's investigation," he said in an email.

According to Payette, the fire was small, located in the plane's exterior generator and quickly extinguished.

When the planes struck, amusement turned to panic on board the WestJet plane, according to passenger Gustavo Lobo.

"Out of nowhere, there was an audible crunch and the plane rocked slightly," Lobo told CBC News on Friday. "We looked out the window and saw that the plane had backed up into us. Everyone was a little shocked and kind of chuckling at the situation."

They didn't laugh for long, he said.

"Panic set in when [we saw] what seemed to be fuel spewing from the crash. After a couple of seconds the entire thing ignited and it was chaos inside the plane. People screaming and panicking all while the flight attendants shouted to try and control the situation."

Lobo took a video of the fire, and said eventually everybody slid down the emergency slides to safety, although the process was slowed by passengers who insisted on taking their carry-on luggage with them.

Ali Alagheband, also on the flight with his wife and son, 12, said a "big ball of fire" lit up the right side windows seconds after the plane rattled with the force of the collision.

"Everybody was saying the F-word and screaming," Alagheband said, adding that he mostly stayed calm until black smoke seeped into cabin.

"The flight attendants kept saying 'remain seated, remain seated,'" he said.

Fearing they would soon be gasping for air and stuck on the plane, he told his son to stay calm and wear an oxygen mask if one appeared from the cabin's ceiling.

"There was fire and there was fuel in that wing," he said.

'Wasn't a good situation'

A mechanical engineer by trade, he could tell "it wasn't a good situation."

Nobody knew an evacuation was underway until a passenger stood on his seat and yelled that a door had opened, he said.

But as the crowd moved toward the door, some passengers blocked his family's escape.

"I was yelling at people reaching overhead to get their bags. It was ridiculous," he said. "I was literally yelling, 'Get the F off the plane."

John-Ross Parks, 32, was aboard another plane to Fort Lauderdale that was beside the Sunwing aircraft. He was waiting to depart when passengers around him began to complain of a funny smell. Parks said he thought it was just exhaust.

'Air was full of fumes'

But half an hour after the scheduled take-off time, Parks said people noticed something amiss.

"The air was full of fumes," he told CBC Toronto.

As people on the plane grew more restless, somebody looked out the window and saw the burning Sunwing plane.

Parks, who was en route to catch a Caribbean cruise with his mother and grandmother, said his flight was cancelled in the pandemonium.

"I've never seen so many emergency trucks," he said. "Nobody knew what was going on."