Chicago, United States: Approximately 20 people were injured when an American Airlines Boeing 767 bound for Miami caught fire Friday as it attempted to take off from Chicago's O'Hare airport, emergency officials said. 

The blaze broke out on American Airlines Flight 383 -- with 161 passengers and nine crew on board -- as the plane was on the runway at one of the nation's busiest airports. 

"We transported about 20 patients with minor injuries to several hospitals," Juan Hernandez of the Chicago Fire Department told a news conference.

He described the injuries as bruises and ankle injuries incurred as passengers exited via emergency slides. 

"We are taking care of our customers and crew and are re-accommodating our passengers on another flight to Miami this evening," American Airlines said in a statement.

The cause of the incident was not immediately clear, with the Federal Aviation Administration and the airline offering conflicting information. 

The FAA said the plane suffered a tire blowout, but spokesman Tony Molinaro told AFP that that information was preliminary and based on initial reports from the plane's pilots.  

In a separate statement, American Airlines blamed the incident on an "engine-related issue." 

Timothy Sampey, with the Chicago Fire Department's airport operations, said the fire was in one of the plane's engines. 

"There was substantial fire on the starboard (right) side of the aircraft," he said. "There was substantial fuel leak."

Officials did not explain the cause of the leak, saying it would be determined by the ensuing investigation. 

Bystanders posted photos and videos on social media showing black smoke billowing from the airliner. 

One video showed passengers coming down emergency slides and running away from the aircraft, with black smoke and flames visible on the right side of the plane. 

Emergency crews surrounded the jet, which appeared to be intact on the runway, though its right side and right wing were charred. 

The FAA said it was investigating the incident and the National Transportation Safety Board had been notified. 

Service was not interrupted at O'Hare, but the FAA said delays were expected.