Farmer dies in VIC storms

A dairy farmer is dead and hundreds of thousands of properties remain without power in Victoria after storms knocked down transmission towers and lines.

A dairy farmer has been killed and hundreds of thousands of homes and businesses remain without power after Victoria's destructive storms.

The 50-year-old man was struck by debris while working on a roof at a property in Darlimurla in South Gippsland on Tuesday, police say.

He died at the scene.

WorkSafe is investigating the exact circumstances of his death, while police will prepare a report for the coroner.

Emergency Management Commissioner Rick Nugent said the nearby township of Mirboo North became isolated in the storms through road closures, with the Country Fire Authority stepping in to supply water.

The community has since been reconnected.

Premier Jacinta Allan said the storms inflicted significant damage statewide, with wind and trees taking down power lines and collapsing transmission towers near Geelong.

The disaster is one of the largest power outages in Victorian history and could take weeks to fully fix.

At its peak about 530,000 properties were left without power due to the damage from storms, strong winds and lightning.

That number had dropped to 198,000 by midday on Wednesday, but authorities warn further progress could be slow.

Generators could be sent out to communities expected to remain off the grid beyond 48 hours.

Storm damage is to blame for the outages and not the fallen transmission lines, Australian Energy Market Operator chief executive Daniel Westerman said.

Electricity network crews have restored power to a large number of properties following yesterday's severe storms. 

"It sent shock waves through the transmission system," he told reporters.

"We didn't lose any customer supply because of that event."

The collapse tripped about 2800 megawatts of generation offline, along with about 1000MW of appliances and lights, forcing AEMO to instruct operator AusNet to reduce its load.

In doing so, roughly 90,000 customers were kicked off the network in the first 30 minutes.

"That was a system security issue and not because we didn't have enough generation," Mr Westerman said. 

Loy Yang A generates about 30 per cent of Victoria's power.

The station's owner, AGL, said two units had returned to service as of Wednesday morning.

The others were expected to progressively come back online in the next 24 hours, it said in a statement to the stock exchange on Wednesday morning.

The network disruption pushed the spot power price in Victoria and Tasmania to its ceiling of $16,600 per megawatt hour, hundreds of times higher than typical levels.

Dozens of schools and early learning centres across Victoria were closed on Wednesday because of fire warnings or power outages.

The widespread outages also sent the train network into disarray and cut power to traffic lights.

The security of Australia's energy network is increasingly coming under threat from more destructive and frequent severe weather events fuelled by climate change, the premier said.

Energy Minister Lily D'Ambrosio said the national system needed to be more resilient.

"Poles and wires just don't stop at the borders, transmission lines don't stop at the borders."