AAP said Victoria's State Emergency Service was responding to hundreds of calls for help, and thousands of properties were without power.
More than 370 calls were made to the SES in the 24 hours to 12.30pm (local time), with 283 requests still outstanding. The majority were for flooding and building damage.
About 4300 Victorians are without power due to lightning strikes, the energy companies' websites reveal.
At Flemington Racecourse, home of the Melbourne Cup, the rain forced delays to some early races and of some trains to the course.
The area was drenched with more than 46mm of rain before 12.30pm, prompting fears jockeys and horses were at risk of injury, news.com.au reports.
Jockeys complained they were unable to see at times during the first race and a section of roofing collapsed in the press room after water made its way in.
There were also reports of flooding around the track, including in the horse tunnel.
Despite fears by some race-goers the meeting might have to be cancelled, track stewards said they were confident the weather would clear and the feature race would be run on time at 3pm (local time).
The track has been downgraded to heavy and the weather, which has now improved dramatically, has changed the betting market significantly.
Yucatan, which has been favourite for the last few weeks, has drifted out to $7.50 from $6. The new race favourite is noted wet-tracker Magic Circle at $6, Stuff reports
