A severe thunderstorm has hit Melbourne with warnings of heavy rainfall, flash flooding and large hailstones within the next few hours.
Black clouds and large thunderbolts are sweeping across the CBD, breaking the city's spell of balmy weather.
The SES has warned motorists travelling in bushfire-affected areas of the state to be alert to the increased risk of landslide and debris on roads.
Up to 20 millimetres of rain is predicted in areas including Kinglake, Whittlesea and Wangaratta, with the SES warning that rainfall runoff may contain soil, ash, trees and rocks.
The Bureau of Meteorology has also released a severe thunderstorm warning for flash flooding and large hailstones in areas including Daylesford, Castlemaine, Kyneton and Bacchus Marsh.
Phil King, a senior meteorologist at the Bureau of Meteorology, said up to 10 millimetres of rain was expected in the CBD, but Gippsland is expected to receive up to 30 millimetres.
"Most of the storm activity today is going to intensify as it goes further east so I think we'll see the best falls today through the eastern half of the state," Mr King said.
"Now looking out my window it's incredibly dark. Our lightning system is indicating there's a good line of thunderstorm or lightning, it extends back up past Ballarat right across the bay.
"I think by early afternoon, say two o'clock most of that activity will be to the east of Melbourne."
Storm damage, debris and signal faults caused by lightning strikes are slowing the city's trains down.
Connex spokesman John Rees said there were delays of about 15 minutes on the Belgrave, Lilydale, Alamein, Glen Waverley, Epping, Hurstbridge and Sandringham lines.
"The trains are running but they're delayed because of things like debris across the line,'' Mr Rees said.
Melbourne Airport also closed its tarmac for a short time this morning.
A spokeswoman said passengers could expect some delays and should contact their airline directly.
An unusually warm April night had Melburnians tossing and turning in bed last night.
The mercury briefly dipped to a low of 21.2 degrees in the city at 3am after sticking around the mid-20s mark up until midnight, and then rose to 25 degrees by 6am.
It was the third warmest April night in the past 30 years - slightly warmer nights occurred in 2005 and 1985 - and fell short of the highest-minimum April record set in 1966 of 23.4 degrees.
Yesterday's maximum of 32.8 degrees made it the hottest April day since 2005. The record April maximum was set in 1938, when the temperature reached 34.9 degrees.
But Mr King said today's cool change would hit Melbourne by mid-morning, dropping the temperature to the high-teens.
Showers and temperatures in the high-teens are forecast until next Thursday, when the temperature is expected to hit 22 degrees.
