A 21-year-old man is dead and a 23-year-old man critically injured after two small Cessna 152 planes collided in mid-air over Saint-Bruno on Montreal's South Shore.

The injured pilot's life is not in danger, Longueuil police said. Two other people were also taken to hospital for shock.

The crash occurred above the Promenades Saint-Bruno shopping centre shortly before 1 p.m. Friday. One of the planes fell into the shopping centre's parking lot, while the other crashed on the building's roof.

Longueuil police said the pilots of both planes were flying alone.

Firefighters stand on the roof of shopping centre where one of the planes crashed. (Charles Contant/CBC)

Weather conditions were clear and the cause of the crash is under investigation.

"Right now we have investigators at the scene who are trying to verify all hypotheses," Colagiacomo said.

"We're checking everything out to find out what caused this accident first of all."

Canada's Transportation Safety Board confirmed that the two planes belong to Cargair, a flight and pilot training school based in nearby Saint-Hubert. The company declined an interview request when contacted by CBC News.

Cargair released a statement Friday afternoon that said it was co-operating with investigators from the TSB.

TSB on the scene

Investigators from the TSB arrived on the site of the crash Friday evening. To begin their investigation, they're photographing the wreckage and interviewing witnesses, said Regional Senior Investigator Isabelle Langevin.

Langevin said this is the first time she's investigated a collision where two planes crashed mid-air and landed near a populated area.

During a Friday night news conference, she said the TSB is working to get answers for the families of the people affected by the accident.

"The TSB investigation team is mindful of the survivor and the family who lost a love one," Langevin said.

After investigators finish speaking with witnesses and photographing the scene, the wreckage will be transported to Ottawa for further investigation. Langevin could not speculate on how long the investigation will take.

Staff from the Transportation Safety Board inspect the wreckage of a Cessna 152 that crashed in a Saint-Bruno, Que. parking lot. (Jean-François Vachon/CBC)

'It all happened so fast'

One eyewitness, Carol Pelchat, said she came out of a store and heard two planes overhead.

"I looked up and one of them was making a strange sound," she said.

"I saw them hit and a wing came off one of the planes, which started to spiral, and the other plane crashed."

"It all happened so fast."

Pelchat, who works as a nurse, ran over to the site only to find that police had already arrived.

"They said there was nothing to do, it was too late," she said.

Jonathan Littler, 21, was working at a Canadian Tire in Saint-Bruno when one of the two planes landed in the mall's parking lot. He shares what he saw. 0:47

Another witness, Patricia Bon, told CBC that she heard "a loud boom."

"And then a person screamed at the top of their lungs to go outside right away. I saw a plane that was completely crushed."

Both planes were doused with a fire retardant to prevent them from catching fire.

A lone plane tire fell about 20 metres from mangled plane. Witnesses say they heard a loud boom from crash above mall <a href="https://t.co/VwlbFa5TYv">pic.twitter.com/VwlbFa5TYv</a> —@salimah_shivji

Police said a large perimeter has been set up and they are asking people to avoid the area located at the junction of highways 116 and 30. They are asking witnesses to go to the Cage aux Sports restaurant to speak to police.

The shopping centre is closed and will remain closed Saturday.