A massive power blackout has hit Victoria with nearly 350,000 residents and businesses without power.

Homes and businesses in Sunshine, Melton, Woodend, Laverton, Werribee, Geelong, Torquay, Docklands, South Melbourne, Albert Park, Fishermen's Bend, Brunswick, Northcote and Westgate have been hit by outages.

The city's bright lights have dimmed with entertainment hotspots including the Docklands affected and traffic lights on Kings Way out.

The blackouts follow an order from the nation's power wholesaler that Victorian power supplier, SP AusNet, shed 1000 megawatts to "ensure system security'' after a plant failure.

The cut has left 276,000 CitiPower customers and 63,500 Powercor customers in the dark.