Emergency crews are working to restore power supply to about 8,500 people in the Blue Mountains.
Endeavour Energy responded to the outage after lightning strikes struck power lines earlier this afternoon.
Lightning interrupted power to homes and businesses in Springwood, Winmalee, Faulconbridge, Valley Heights, Linden, Hawkesbury Heights and Sun Valley.
“Emergency crews are currently patrolling the area to commence the restoration process,” an Endeavour Energy spokesman told The Daily Telegraph.
“Until these patrols are completed it is not possible to give an estimate of the time it will take to restore power supply to affected customers.”
He urged people who require power for medical equipment to check their battery supply and “consider acting on their back up plan”.
Endeavour Energy thanked residents for their patience as they attempt to restore power.