This is the heart-stopping moment an old woman grabs her granddaughter by the leg after she faints and almost topples off a tall building.

The CCTV camera images were captured on a rooftop terrace in the prefecture-level city of Yueyang in the province of Hunan in the People’s Republic of China recently.

The footage shows the young woman walking in the middle of the wide terrace with the older woman reportedly her grandmother just behind her.

She is looking directly at the young woman and realises that she is starting to stagger, and then suddenly topples to the right as the older woman notices something is wrong and runs over to grab her.

Seconds later, the young woman hits the low wall of the roof and plunges over the edge only to be grabbed at the last second by the much older woman who holds onto her leg to stop her falling.

The older woman then screams for help as a man and two young boys rush out and pull the young woman back onto the roof.

They then help her back inside as the boys stare incredulously at the drop and the young woman is helped back inside.

The footage went viral after it was shared online with people praising the quick reactions of the old woman in saving her granddaughter’s life.