Customer foils Sydney attempted robbery

A quick-thinking customer has foiled an attempted armed robbery in Sydney's north-west.

A man stormed a Rouse Hill service station at about 11.45pm on Saturday and threatened staff with a gun.

Police say the would-be thief became engaged in a scuffle with a male customer who detained him until officers arrived.

The gun-wielding man was taken to Westmead Hospital with minor injuries sustained in the altercation.

He remains under police guard.