A New York bus driver has become a surprise hero after saving a seven-year-old girl who accidentally fell three stories from a Brooklyn apartment building.

"I just said 'Please, let me catch her, lord, please let me catch her," Stephen St. Bernard told local NY1 television about Monday's rescue in the Brooklyn's Coney Island neighbourhood.

A video of the incident taken on a mobile phone and broadcast by the channel showed the girl standing on an air conditioning unit outside her apartment window more than 30 feet (10 meters) from the ground.

Amid cries from people watching the scene unfold from the ground, the girl fell into the arms of St. Bernard.

"I ran over there hoping that she wouldn't fall. When I got there, she was still standing there and I just positioned myself," he said.

"When she lost her balance, I caught her. She has no scratches or anything. She's okay."

St. Bernard, who said he cried after saving the girl, suffered a torn tendon in his arm from the impact.

The girl has been identified as Keyla McCree. Her mother had left her alone in the room moments before, according to the New York Post.