Torrential rain lashing much of NSW is threatening widespread flooding as the State Emergency Service prepares for the fallout from days of wild weather.

The Bureau of Meteorology said central NSW received more than 44 millimetres of rain on Wednesday as thunderstorms and pelting rain hit much of the state, with the deluge predicted to last another two days.

Some areas are tipped to receive a month’s rain by the end of the week.

SES Assistant Commissioner Dean Storey said units were in a heightened state of readiness on Thursday, with extra support and resources already deployed to at-risk areas, including flood-risk strike teams and aviation support.

“A large proportion of the state [is expected] to be affected, which will result in flash and riverine flooding in many areas, potentially up to major level as well,” he said.

“The SES is urging communities to be aware of your local forecasts, monitor the local reports from the bureau, know your local risk.”

After a wet winter, catchments are wet and dams are full, so any heavy and sustained rain could quickly lead to flooding.

“The SES is poised and ready to support our communities as it always does,” Mr Storey said.

“We’re just urging those communities and the public to do their part.”

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The Riverina is already flooding. Widespread flash flooding is predicted and the SES is asking people living in flood-prone communities to prepare now.

Mr Storey said roads were expected to be cut in many areas and advised people to avoid unnecessary travel and never drive through floodwaters.

“Time and time again we see poor results with poor decision making with people driving through floodwaters, often with tragic results and our emergency responders are at high risk as well,” he said.

The north-west slopes and plains, Northern Tablelands, central-west, south-west slopes are all in the firing line with the communities of Moree, Armadale, Tamworth and Parkes singled out to be on high alert for flooding.

“They are particularly the focus but this weather event is going to impact a large proportion of the state,” Mr Storey said.

There are 18 flood watches in place and three flood warnings that will likely increase is at the day goes on.

The rain across NSW and Queensland comes after the same system has already drenched central Australia. On Wednesday, a man spent six hours trapped in Alice Springs’ Todd River after his car was swept off a causeway.

More than 90 millimetres of rain saturated the region on Tuesday, followed by about 50 millimetres more on Wednesay.

-with AAP