Driver accused of causing car accident that left mother and child trapped under active power lines

Western Australia Police allege a driver accused of causing a car accident in the state's south fled the scene leaving a mother and her child trapped under active power lines.

Police say the driver of a Mitsubishi Triton ploughed into a power pole on Anstruther Road in Mandurah around 9.30pm yesterday.

Nearby residents rushed to help, but the man behind the wheel had already run off.

The impact of the crash had downed lines, leaving live power lines hanging dangerously over the street.

With the street pitch black and the power lines down, a woman with her young son in the car unknowingly continued driving forward.

"I saw the first car trapped in there, because as I was running I had the torch and I saw her coming and I was like 'stop, stop, stop', and then I saw her get straight into the power line," witness Trevor Donohoe told 9News.

The mother and son were stuck under the wires for half an hour.

"The police told them to wind up the windows, turn off their mobile phones and stay in the car," witness Shona McCullough told 9News.

The pair were finally freed by firefighters.

Western Power spent more than 15 hours attempting to restore electricity to 1700 homes.

The driver has handed himself in to Mandurah Police.