A pedestrian walks along a flooded street
© Julian Smith/EPA
A pedestrian walks along a flooded street in the south of Melbourne on Thursday
Seventeen people have been rescued by helicopter and 100 people are stranded in their cars on a flooded Hume Highway in northeast Victoria.

With more than a month's worth of rain already fallen across parts of northeast Victoria as wild weather rages across the state, authorities say some people have not heeded warnings about driving into floodwaters.

"We've seen people that have had to be rescued from the roofs of their cars, 17 people in total, and 100 people have been stranded just to the south of Wangaratta," Victoria State Emergency Service chief officer Tim Wiebusch told reporters.

"Early indications is the Hume Highway will be impacted for another 48 hours, that's particularly on the southbound lanes of the Hume Highway, just south of Wangaratta, so people are advised to check the VicRoads website for traffic diversions in those areas."

The moisture from tropical Cyclone Owen is feeding the low-pressure system over Victoria on Thursday, which is forecast to bring heavy rain and thunderstorms.

The Bureau of Meteorology says there's been record-breaking rainfall across the state's northeast in the 24 hours to 9am Thursday and the few hours since, including 162mm at Everton and 110mm at Eldorado.

The downpour is due to bring the average December rainfall of 59mm in one hit.

The SES has received more than 400 calls for help, with 300 of those dealt with.

"There is a risk of thunderstorms mixed up with the rain today, which will add to the extreme rainfall and flash flooding risk across the state," Bureau of Meteorology senior meteorologist Rod Dickson said on Thursday.

"But also the potential for some damaging winds and some hail, particularly for the north east of the state, later today."

Hail stones about 2cm in size could fall as damaging winds gusting up to 90km/h sweep through the warning areas.

On Thursday the bureau also issued a severe weather warning over much of New South Wales, with Sydney expected to be hit by a storm on Thursday evening.

The warning covers an area stretching from the state's northern to southern borders, with damaging winds and heavy rain that may lead to flash flooding and large hail already affecting parts of the state.

The bureau said thunderstorms were being caused by warm humid air feeding into a trough on the state's western plains, combined with an upper low pressure system entering the far southwest.

"There is a risk for destructive winds and giant hailstones in isolated storms in the warning area," it said.

"Locations which may be affected include Gosford, Sydney, Wollongong, Armidale, Orange, Canberra, Goulburn, Tamworth, Moree, Dubbo, Wagga Wagga and Albury."

A severe weather warning for heavy rain is also in place across most of Victoria.

The State Emergency Service received almost 250 requests for help in the 24 hours to 10.30am on Thursday, mostly for flooding, building damage and fallen trees.

Rainfall is expected to continue on Friday, with some parts of the state likely to get 20mm to 50mm, while the Gippsland Coast and Otway Ranges are bracing for more than 100mm.

Owen, currently a category three storm, is expected to grow into a destructive category four before it crosses the Queensland coast on Friday.

Heavy rain in Melbourne also forced the cancellation of the women's quarter-finals in the Australian Open wildcard playoff. The women's matches have been rescheduled for Friday morning, starting at 10am, and will be followed by the men's semi-finals.

Source: Australian Associated Press