Melbourne Cup racegoers set to cop another drenching on commute home

The temperature is expected to drop from 20 to 15 degrees, and the skies are set to open up again.

"They actually got lucky down at the track," Bureau of Meteorology senior forecaster Michael Efron said.

A line of showers is moving through the western suburbs and is expected to reach Flemginton, drenching punters as they leave the track.

The downpour, however, is set to ease in the evening.

More than double the predicted 15 millimetres of rain fell at Flemington, with the gauges reading 38 millimetres not long after 9am.

Metro Trains crews had to pump water from the train tracks on Platform 1 at Flemington after they were flooded in the early morning downpour.

In a bid to minimise the delays, a number of trains were stopped at Melbourne Showgrounds, meaning punters had a six-minute walk in torrential rain to get to the track.

Frocked-up punters took off their shoes - and in some cases, their pants - as they waded through floodwaters on their way to the race. Others donned ponchos and clutched umbrellas as they tried to dodge the mud and puddles.

It won't come close to the wettest Melbourne Cup day, though, which was in 1942 when 46.5 millimetres of rain fell.

On the record-breaking front, it also won't be the hottest or coldest.

The hottest Melbourne Cup was 35.1 degrees in 1902 while the coldest was in 1913 when racegoers shivered in 11 degrees.

Away from the track, flash flooding caused chaos along Kingsway, at the tunnel entrance onto the CityLink, as well as in parts of Southbank and Rowville.

Some motorists were left pushing their cars through the floodwaters.

Elsewhere in the state, 30 millimetres of rain was expected to fall within just two or three hours, but some areas were drenched with more than 60 millimetres.

Sunbury, in Melbourne's north-west, has been soaked by more than 60 millimetres of rain since 9am on Monday, while a severe weather warning has been issued for Central, North Central, North East, West and South Gippsland and parts of East Gippsland and Northern Country Forecast Districts.

Cardinia, 52 kilometres south-east of Melbourne, was also hit by more than 62 millimetres overnight.

The weather also caused flight chaos on Tuesday, with flights bound for Melbourne from Singapore and Japan having to be diverted to Sydney after heavy rain and cloud forced a runway closure.

A Virgin Australia spokeswoman said the Melbourne Airport tarmac was closed for 45 minutes on Tuesday morning, leading to flight delays of up to an hour across most airlines.

A wintry blast is expected to move in across the state late Tuesday night as a low pressure system sweeps the state.

"We're only expecting a top of about 16 on Wednesday and it will feel a lot colder because there will be fresh westerly winds and the chance of hail and thunderstorms," Mr Efron said on Monday afternoon.

"We're even expecting some snow to develop in elevated parts of the state including the Grampians as the cold air moves in."

However, the clouds are set to part, and it will be a partly sunny and dry 18 degrees on Oaks Day.

Temperatures are expected to creep back up into the low 20s by Friday, with the mercury tipped to hit a warm 21 degrees on Saturday for Stakes Day.

With AAP