Flash flooding wreaks havoc across Melbourne's south-east

Flash flooding wreaked havoc across Melbourne's south-eastern suburbs last night, with streets turning to rivers from Clayton to Dandenong.

There were more than 300 calls made to the SES, including 50 in the Springvale, Mulgrave and Keysborough area.

A number of motorists had to be rescued after their vehicles became trapped in flood waters.

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Owners of a BP service station in Mulgrave tried to save their equipment as waves lapped the business.

Operator Ayush Tyagi said the incident was "pretty crazy".

"At first it felt a bit unreal," he said.

"Especially when you work at a service station you have that fear of a potential leak of fuel, so, yeah we were scared."

The heavy rainfall and hail even led to water seeping into Chadstone Shopping Centre, where shoppers were seen jumping in puddles indoors.

While there wasn't a huge amount of rainfall in the past 24 hours, it fell quickly, with some areas like Springvale recording 23.4mm in just 13 minutes.

SES Volunteer Meg Peach said the organisation had experienced its two busiest periods ever in the past six months.

Sydney saw thunderstorms today, with multiple warnings issued this afternoon and continuing into the night for parts of the west.

Passengers on the Manly ferry were in for a rough ride.

Terrey Hills on the Northern Beaches got 11mm of rain, with showers to continue across the city for much of the week.