UPDATE, 8.30pm: BOTH potlines at the Portland Aluminium smelter are operating at about half capacity, an Alcoa spokeswoman said.
She said power was lost at 2.24pm and was restored to potline two at 5.10pm and potline one at 5.40pm.
"Both lines are currently operating at about 55 per cent of line load," the spokeswoman said.
"The dedicated smelter team continues to focus on the safety of our people."
UPDATE, 8pm: CLIMATE researchers have weighed in on the damage to south-west infrastructure from storms on Friday.
University of Melbourne researcher Dylan McConnell said the event showed "extreme weather, intensified by climate change, is disrupting critical services and infrastructure".
"This incident underscores the urgent need to decarbonise our energy system and invest in low-carbon solutions ... to minimise the chance of such costly and potentially dangerous energy disruptions in the future," he said.
UPDATE, 7:05pm: WORKS could be lengthy to repair six downed towers and two others with "extensive damage" following storms near Cressy on Friday afternoon, power company Ausnet Services says.
"We have crews at the site making the area safe and assessing the extent of the damage," a company spokeswoman said.
"We will work to repair and reconstruct these lines as soon as possible, given the extent of the damage it will take some time."
UPDATE: 6.10pm: A STORM cell that tore through the Cressy area on Friday afternoon has left a trail of destruction, a firefighter says.
District Six operations officer Mark Gunning said there was damage to a number of properties and power lines.
"An eyewitness reported the sky turning black and square hay bales flying down the road," Mr Gunning said.
"Iron has been ripped from roofs and is around paddocks."
He said there were six high voltage power lines "ripped out of the ground" north of Cressy, and damage to at least one other.
UPDATE 5.45pm: POWER has returned to the Portland smelter with both potlines now back online.
Portland-based Australian Workers Union organiser Rob Saunders estimated the power had been lost for about three hours.
He said any damage to the potlines would unlikely be fully understood until Saturday.
"Now the power is back it's all hands on deck, they are trying to massage these things back into life," he said.
But he said the site was only receiving half of its required power.
"Trying to maintain the pots at half power is really difficult so they're working hard at that," Mr Saunders said.
"There's still plenty of hope and optimism but they know its a hard road ahead."
EARLIER: DAMAGE to a number of south-west transmission lines has caused the Portland Aluminium smelter to lose power.
A spokeswoman for power company Ausnet Services said the damage had been on the Moorabool to Mortlake and Moorabool to Tarrone transmission lines.
"This has resulted in a separation between Victoria and South Australia at the Heywood interconnector and an interruption to supply to the Portland aluminium smelter," she said.
"There are reports the damage was caused by a storm event but this is not yet confirmed."
Portland-based Australian Workers Union organiser Rob Saunders said power at the smelter had been out for a number of hours, and workers were waiting for it to resume.
"There's nothing they can do until they get the power," he said.
"It's always the risk with the smelter if you don't have power, it solidifies in the smelting pots and that's the end of the game."
He said an attempt was under way to "start up the Mortlake Gas Station and direct that electricity to the smelter".
It follows another power outage in November when power was lost to the smelter's potlines for between four and eight hours.
"Unfortunately the site is quite experienced in these events and they are exceptionally good at maintaining their process," Mr Saunders said.
The Bureau of Meteorology has issued a severe thunderstorm warning for the south-west of the state.
The Department of Transport has advised motorists to slow down in the wet, to be extra-vigilant when behind the wheel and to avoid driving through floodwater.
It warned drivers should leave extra space between themselves and the car in front, as braking distances increase in wet conditions.
The use of headlights is recommended to help see and be seen. Drivers should look out for cyclists and motorbikes which can be harder to see.
If the rain becomes too heavy for wipers to cope, the department suggest pulling over safely and waiting for the rain to pass.
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