Flash flooding has inundated parts of western NSW, with heavy rain falling on some drought-ravaged areas and predictions of more wet weather to come.

Key points: Towns like Dubbo, Walgett and Coonamble have received between 20 and 40 millimetres

Towns like Dubbo, Walgett and Coonamble have received between 20 and 40 millimetres Another system further east will bring intense rain and the risk of flash flooding to northern NSW

Another system further east will bring intense rain and the risk of flash flooding to northern NSW Despite predictions, the rain is unlikely to be enough to break the state's drought

A trough has delivered welcome falls near Cobar, Bourke and Nyngan, and has also given some farmers around Dubbo, Parkes and Moree reason to smile.

A 10-kilometre stretch of the Kidman Highway is under water and closed between Cobar and Bourke.

Bureau of Meteorology (BOM) duty forecaster Mike Funnell said towns including Dubbo, Coonamble, Dunedoo, Gilgandra and Walgett had recorded about 20 millimetres so far but some agricultural gauges had picked up about 40mm.

Roads near Nyngan are now under water. ( Facebook: Robyn Cashion )

The rain band is a result of a steady flow of warm moist air coming from a system in Queensland.

Over the next five days, it will provide some areas with the most rain they have seen in a long time, Mr Funnell said.

But unfortunately the Murray-Darling Basin is so rain deficient, the falls will not make for significant inflows, according to the BOM.

The BOM said a separate high-pressure system would also combine to draw tropical conditions down Australia's east coast as the week progressed.

Heavy rainfall has meant Kidman Way between Bourke and Cobar looked more like a river. ( Facebook: Outback Radio 2WEB )

A severe weather warning has been issued for the Mid-North Coast and Northern Rivers with intense rainfall on Wednesday and Thursday.

The BOM said there was a risk of flash flooding.

"Flash flooding will become quite a risk, particularly if we get these storms over the same areas day after day," BOM forecaster Dean Narramore said yesterday.

"As we get into the weekend and early next week, we could even possibly see riverine flooding for some parts of NSW as well, and even possibly in the southern parts of Queensland."

BOM forecaster Bimal KC said Sydney and the South Coast could also see over 50mm from now until Monday, but would not see significant falls until Saturday.

Catchments including the Warragamba Dam are expected to receive new inflow and rain is also set to fall over firegrounds around Bega and help to extinguish some of the bushfires across the state.

However, the RFS has previously said vegetation and trees in fire-affected areas were prone to significant run-off, which could lead to flooding.

The rain is not expected to be enough to break NSW's drought, which continues to affect every part of the state.