Media playback is unsupported on your device Media caption Footage shows emergency crews at the scene, as Geeta Guru-Murthy reports

A Chicago metro train has derailed at O'Hare International Airport, injuring 32 people, officials say.

Early on Monday the train came off the tracks, crossed a platform and travelled part way up an escalator at one of the busiest airports in the US.

None of the reported injuries are serious.

The president of the Chicago transit union told reporters the train operator was "extremely tired" and may have dozed off in the train's cab.

And authorities have said the train was travelling too fast when it crashed.

"I heard a boom and when I got off the train, the train was all the way up the escalator," passenger Denise Adams told the Chicago Sun-Times newspaper.

Fire officials told the Chicago Tribune that six people were in fair condition and 26 in good condition as they were transported to hospital.

Investigators are said to be reviewing security footage and interviewing CTA employees to determine the cause of the derailment.

They plan to interview the train driver, who remains in hospital.

Image copyright AP