Delta plane crash investigators piece together Toronto Airport incident

Investigators probing Monday afternoon's Delta Flight 4819 plane crash at Toronto Pearson International Airport are piecing together what caused the dramatic incident in which at least 18 people were hospitalized, sources have told ABC News.

The Delta regional jet -- a CRJ 900 aircraft operated by Endeavor Air -- originated in Minneapolis. The aircraft was left lying upside-down and ablaze on the snow covered Toronto runway after the crash, with its 76 passengers and four crew evacuated, according to Delta and the Federal Aviation Administration.

Toronto Pearson President and CEO Deborah Flint confirmed there were no fatalities, commending the "heroic and trained professionals" who responded to the crash. Flint added there were 22 Canadian citizens among the passengers.

At least 18 people were taken to hospitals but Peel Regional Paramedic Services said none of the injuries were considered to be life-threatening.

Three people suffered critical injuries -- one child, a man in his 60s and a woman in her 40s -- according to medical transport organization Ornge. The child was transported to the Hospital for Sick Children and is listed in good condition, the hospital said Monday evening.

Twelve other people sustained mild injuries, Peel Regional Paramedics Services said.

What caused the plane to flip and catch fire was not immediately clear. Sources told ABC News on Monday that the investigation was already underway.

The Transportation Safety Board of Canada will lead the investigation and investigators from the FAA and National Transportation Safety Board are assisting.

The Toronto Airport temporarily stopped flights in the wake of the crash, with departures and arrivals resuming at 5 p.m. ET Monday, the airport said. Two runways remained closed, which Flint said may impact operations.

Delta said its "primary focus is taking care of those impacted."

Delta CEO Ed Bastian said in a statement, "The hearts of the entire global Delta family are with those affected by today's incident at Toronto-Pearson International Airport. I want to express my thanks to the many Delta and Endeavor team members and the first responders on site."

The crash occurred during blowing snow and strong wind gusts in the region. Winds reached 40 mph on the ground and were even stronger several hundred feet in the air.

Toronto Airport Fire Chief Todd Aitken said the runway was dry and there were no crosswind conditions at the time of the crash.