The Bureau of Meteorology (BOM) says Tasmania, Victoria and NSW are in the firing line as widespread heavy rain and damaging winds descend, bringing potential for major flooding.

BOM has issued flood watches in Victoria and Tasmania, where rainfall may top 300mm in 24 hours in elevated areas, and severe weather warnings for large parts of south-east Australia.

Central and northern Victoria and southern inland NSW are set to be hit by 30-50mm of rain in six hours overnight and into tomorrow (October 13).

“This warning has now been expanded to include Melbourne and northeast Victoria,” Senior Meteorologist Jonathan How said. “For Melbourne, the main risk of flash flooding will come on Thursday afternoon and into the evening.”

Falling on wet or already flooded catchments, the latest downpour will lead to renewed river and creek rises, and BOM says moderate to major flooding is likely across northern and central Victoria and northern Tasmania.

Tomorrow, 120mm of rain in 24 hours is possible over elevated terrain in Victoria, increasing the risk of landslips and debris across roads. Northern Tasmania should expect heavy rain, with six hourly totals of 40-60mm and up to 100mm across the Great Western Tiers, overnight and into tomorrow.

Damaging winds above 90km/h are forecast for elevated areas of central and eastern Victoria from tomorrow morning, and from the afternoon in NSW’s Alpine regions and Tasmania's north-east and eastern coasts.

Residents near rivers, creeks and streams or in low lying areas, especially in northern Victoria, Tasmania and NSW’s Riverina, are advised to monitor warning updates.

This year, Sydney is experiencing its highest annual rainfall on record, and floods in NSW and Queensland in February and March became Australia’s costliest flood, with insured losses of $5.45 billion from 234,000 claims. The 1999 Sydney hailstorm is the only Australian catastrophe to cost insurers more.