A bystander has filmed the moment a neighbour saved a seven-year-old US girl from injury after she fell from a third-storey window.

Brooklyn resident Steven St Bernard, 52, suffered a torn tendon in his bicep when he caught little Keyla McCree in his arms yesterday, the NY Post reports.

Keyla, who has autism, had squeezed through the gap between a new air-conditioner and the window frame.

Mr St Bernard said she stood on top of the air-conditioner for a moment 'dancing and smiling' before falling.

'There were all these kids yelling, 'the little girl, the little girl',' said Mr St Bernard, a city bus driver.

'I saw a little girl standing on the air conditioner. I said, 'Let me get over to her in time. And I made it just in time.'

Her mother Shaleema McCree said Keyla was fine.

'Not a scratch on her. The man caught her, thank God. It's a miracle.'.