The weather bureau has warned looming wild weather could dump hundreds more millimetres of rain, after intense storms wreaked havoc across three states on Wednesday.

Homes were flooded in NSW as a system brought 24 hours of rain that caused flash flooding and dramatic rescues after cars were swept away.

One of the worst hit areas was Lake Conjola, on the NSW south coast, which recorded 351 millimetres.

The Bureau of Meteorology’s Kevin Parkyn said parts of Victoria’s Gippsland and the Otways were next in the firing line and could get as much as 200 millimetres of rain in 24-36 hours.

“Where we do see this intense rainfall, it will result in flooding,” he said.

Parkyn said there would already be minor to moderate flooding in many catchments. Heavy rainfall on Thursday could make it major flooding.

People living in rural and low-lying areas are urged to prepare as their areas could face potential evacuations and flooding.

“We’ll also see a range of roads that will be cut, particularly local roads, but we may also see some major roads in Gippsland being cut over the next 24 to 48 hours,” Victorian SES boss Tim Wiebusch said.

Some parts of northern Victoria had more than 80 millimetres of rain in the 24 hours to Wednesday night, which is unusually heavy for this time of the year.

Swan Hill, near the Victorian border, where residents woke to find streets inundated with floodwaters on Wednesday morning, had recorded 85 millimetres in 24 hours by nightfall.

Victorian SES personnel responded to more than 300 calls for help across the state from late Tuesday into early Wednesday, with most relating to trees falling onto roads as a result of strong winds, Wiebusch said.

The situation had eased by Wednesday night. But the SES was still dealing with more than 140 active calls for help across the state at 7pm.

Eastern NSW was hit with heavy rains and destructive winds late on Wednesday, with the BOM also warning of large hail and flash flooding in severe thunderstorm warnings.

Two people were rescued after their car was swept away in floodwaters and others from a NSW home.

The NSW SES had fielded about 900 calls for help in the 24 hours to Wednesday night, and about 600 since midday.

Most calls were about floodwaters threatening properties, leaking or damaged roofs and fallen trees, with a significant number of calls coming from the state’s southeast.

“That does seem to be the area continuing to be affected overnight with the weather still a risk,” NSW SES spokeswoman Jenni North said.

Emergency crews earlier responded to seven rescues with more than 20 homes affected by flooding at Deniliquin, in NSW’s south-west.

Five “in-water” strike teams of 20 highly trained firefighters were being sent to NSW’s saturated south coast to help with flood rescues overnight.

A storm lights up the night in south-east Queensland on Wednesday.

Storms also lashed south-east Queensland on Wednesday. They are expected to ease on Thursday, before returning on Friday.

There were multiple flood warnings for Queensland on Wednesday night.

At the other extreme, severe heatwave conditions in north Queensland are expected to build along the east coast and extend south before easing on Friday.

Some far north Queensland centres have endured a string of days in the mid-to-high 30s. They are forecast to continue to at least the end of the week.

-with AAP