Many offices throughout the city have closed, events have been cancelled and people are being warned not to travel as Melbourne prepares for extreme rain and flash flooding.

Several businesses on flood-prone Southbank have also closed their offices and told people to work from home. Other businesses sent workers home at midday on Friday.

VicRoads is urging people to stay out of the city as a severe storm front bears down across the state, bringing possible flash flooding. Its warning has been extended to its employees who have been instructed to work from home and avoid the commute to the Kew head office.

"We do need to follow our own warnings," Chris Miller from VicRoads Traffic Management Centre said.