People in more than 80 Melbourne suburbs have been told to boil their drinking water after deadly storms that swept across the city also contaminated the water supply.

There were reports of panic buying of bottled water at supermarkets across Melbourne’s east after the warning, which came after a night ofwild weather, which left three people dead – including a four-year-old boy.

The boy suffered critical injuries after being crushed by a tree in suburban Blackburn South on Thursday night. He was rushed to hospital but later died.

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The others to be killed were a 59-year-old man, who died after a falling tree smashed onto his car in Melbourne’s east, and a passenger in a ute travelling on the Maroondah Highway, north-east of the city.

The 36-year-old woman was killed when a tree fell onto the ute. The 24-year-old male driver was taken to hospital with minor injuries.

The storms moved across Victoria from the south late on Thursday afternoon. They crossed Melbourne and headed for north-eastern Victoria from late in the afternoon into the night.

• See a full list of affected suburbs here

Damage caused by the storms led to undisinfected water from Silvan Dam, 40 kilometres east of Melbourne, entering the water supply system.

Yarra Valley Water has issued a contaminated water notice for more 88 Melbourne suburbs on Friday. About 250,000 households have been told to boil their tap water before drinking.

That sparked a rush on bottled water supplies at many Melbourne supermarkets.

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Victoria’s chief health officer Brett Sutton said the water advisory was because some water in the system could not be considered safe after the power outages.

“We do ask households to bring their water to a rolling boil and to use it for all consumption, whether you’re drinking it, using it for brushing teeth, making ice,” he said.

“Just make sure that that water is boiled to a rolling boil before it is used. Obviously let it cool down to make it safe for kids as well.

“It is a very broad boiled water advisory but I hope it is not going to be in place for too long.”

State Emergency Service deputy chief officer Dave Barker told ABC Radio Melbourne it had been “a challenging 18-hour period”.

Mr Barker said suburbs in eastern Melbourne were some of the hardest hit.

“The storm made its way throughout the coastal areas of Victoria, so many parts into Gippsland are impacted,” he said.

Mr Barker said the priority was to move trees off power lines that had fallen across roads.

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Premier Daniel Andrews offered his condolences to the families of those killed.

He noted it was “no ordinary storm event”, occurring against the backdrop of strict COVID-19 rules in metropolitan Melbourne and regional Victoria.

To help people to legally render assistance, Victoria’s health department is issuing detailed advice online as the clean-up could take days.

“That is not an invitation for people to do things that don’t need to be done,” Mr Andrews said on Friday.

“But we do recognise … there will be other needs that will need to be met by perhaps a family member.”

More than 95,000 properties suffered power outages when the storm hit.

Wind gusts as high as 124km/h were recorded at Mount Gellibrand, east of Colac in southern Victoria, and 100km/h at Port Fairy, on the state’s south-west coast.

Ausnet said 52,000 customers remained without power in Victoria’s east, and 600 Powercor customers, mostly in the south-west in the Otway Ranges and towards Colac, were also without power.

In the 24 hours to 8.30am, the SES had received more than 2100 calls for help.

Felled trees made up 85 per cent of the calls and 10 per cent were related to building damage.

More strong winds are forecast for Victoria on Sunday.

Meteorologist Chris Arvier said gusts could reach similar levels to those that battered the state on Thursday and trigger another severe weather warning.

-with agencies