Large chunks of Australia's Victoria state lost power on Tuesday afternoon when a major power plant shut down because a storm knocked out parts of the state's electricity transmission network.

AGL's Loy Yang A power station, responsible for about a third of the state's power, was forced to shut down on Tuesday afternoon after several towers along a major section of the state's transmission network collapsed in bad weather.

More than 500,000 homes or businesses had lost power, state energy minister Lily D'Ambrosio said in a social media post.

As the plant shut down, electricity prices spiked across the state to their maximum of A$16,600 per megawatt hour, up from around A$200, according to data from the Australian Energy Market Operator (AEMO).

In response, AEMO ordered electricity usage cut across the network, according to a statement on Tuesday afternoon.

D'Ambrosio said in her post that one of Loy Yang's four units had been brought back online and the mandatory power cuts had ended.

AGL said in a statement it was working to bring three of Loy Yang's units back online through Tuesday evening.

"We continue to work with AEMO and stakeholders to investigate the cause of the issue."

The failure comes amid repeated warnings from AEMO that urgent investment is required to ensure power supply remains reliable as the country's fleet of aging coal-fired power plants are retired.