Video released of US gas explosion

Amateur shows a huge fire ball roaring through a San Francisco neighbourhood after a gas line ruptured in the area.

Four people died in the explosion and at least 50 people were injured, with seven suffering critical injuries.

The explosion left a giant crater and laid waste to dozens of 1960s-era homes in the hills overlooking San Francisco Bay.

All that was left of some houses were chimneys, rising from still smouldering ruins.

The video, shot through the window of a house, shows a wall of flames passing by the home as its terrified resident is heard screaming profanities.

Officials were trying to determine what led to a blast that raised questions about the safety of similar lines that crisscross towns across America.

Some residents said they had smelled gas in the neighbourhood over the past several weeks.