Victoria could be hit by falls of up to 100 millimetres of rain

The Bureau of Meteorology's weather forecaster Kevin Parkyn said there was a significant rain event "on Victoria's doorstep", with falls of up to 100 millimetres predicted in some parts of the state.

"What I am most concerned about is the intensity of the rain that will peak on the Thursday," Mr Parkyn told a briefing at the State Control Centre.

"We have a short term flash flood risk, as a result of that rainfall intensity, and then a longer term, riverine flooding risk, that will take a while for some of those waters to find their way down river systems."

"We've seen tropical moisture build over the top end of Australia for some time now, that's courtesy of the negative Indian Ocean Dipole, and a third successive year of La Nina."

Excessive moisture in the atmosphere occasionally found its way down to south eastern Australia, he said.

"We saw a pulse of that tropical moisture affect Victoria last week," he said.

"This next burst of tropical moisture is more significant."

It would begin on Wednesday and intensify on Thursday.

There could be storms in the western districts, with localised storms of between 20-30mm, Mr Parkyn said.

"The real concern is the very early hours of Thursday, right through to Friday morning, where we are expecting widespread falls of 20-50mm across much of Victoria," he said.

But there might be higher falls of 60-100mm about the Dividing Range and in the north of the state.

Mr Parkyn said there was a longer term risk of flooding in the Wimmera, Avoca, Loddon, Campaspe, Goulburn, Broken, King and Ovens rivers.

That was likely to occur into the weekend and next week, he said.

"It's not just about rain, though, often these weather systems are accompanied by strong winds, so we are concerned about damaging wind gusts of 90-100 kilometres and hour affecting elevated locations," he said.

"It's not over yet - we are likely to have further incursions of tropical moisture as spring unfolds, leading into summer."

Read more: Wagga, Riverina towns set to flood for second time in as many months

Premier Daniel Andrews said Community Contingency Caches had been restocked, in preparation for the upcoming event.

"We are going to see a significant rain event - we know our catchments are full and we have had record rainfall, to this point, and the ground is absolutely sodden," Mr Andrews said.

"Even a minor amount of rain will be a risk, in terms of flood, but it is not a minor event we are forecasting, there will be significant rainfall in certain parts of the state."

The caches are designed to equip responders and community members with emergency tools including first aid and hygiene essentials, infant supplies, dust masks and respirators, batteries, water, food and cooking supplies, tents, lighting, bedding and equipment needed to set up an emergency base.

Each of the two caches is able to provide relief for up to 50 people in the immediate aftermath of impact from a major emergency for up to five days.

They can be pre-deployed based on predictive services - modelling ahead of significant weather events that points to things like floods or fires, or following emergency events where extended periods of community isolation can occur.

The caches can be deployed via road or components of the caches could also be transported by air, to get emergency supplies delivered to areas in advance of a potential event as quickly as possible.

The government's fleet of emergency helicopters, including six new arrivals, remained on standby to assist with further airlifts of supplies, equipment and emergency personnel as needed.

More than 200 generators were also on standby, ready to be deployed by the Department of Environment, Land, Water and Planning (DELWP) to households facing prolonged power outages after a severe weather event.

They were generators purchased during last year's flood and storm event in June.

Victorians are encouraged to make their own preparations for potential emergencies by having enough supplies on hand to last for up to 72 hours and to set up a support network with friends, family, neighbours and their local council.