Widespread rainfall across NSW is expected through the second half of the week with some areas expected to receive more that a month's worth of rain in three days, according to the Bureau of Meteorology.

Minor flood warnings are in place for the Bellingen and Kalang rivers, Nambucca, Manning and Gloucester rivers.

The heaviest rainfall is forecast to contract to the south east of the state through the weekend as the low moves offshore.

The weather system is expected to cause flooding into the weekend.

Residents are being urged to prepare for potential flooding, heavy rain and thunderstorms for the rest of this week.

Bureau of Meteorology Hazard Preparedness and Response East manager Jane Golding said key areas of concern ranged from Queensland down through to Victoria, and included river catchments close to the NSW-Queensland border and along the western slopes in New South Wales.

"Heavy rain and thunderstorms are expected to set in from Wednesday and continue into the weekend, so we're urging people to prepare now," she said.

"Many areas in eastern Australia will see significant rainfall, and some locations in New South Wales and Queensland are likely to see daily rainfall totals of 150 millimetres or higher.

"This kind of heavy rainfall over a short period of time can cause dangerous flash flooding and combined with the fact that many river catchments down the east coast are already quite wet, there is a very real risk that we may see some rivers flood too.

"Please make sure you're staying up to date with current forecasts and warnings and be careful when you are out and about this week."

Parts of New South Wales are forecast to receive more than a month's worth of rain over the next three days.

"That's why we're warning people early to be prepared for this severe weather system. We want people to 'know your weather, know your risk', have the most up-to-date information, and be factoring our forecasts and warnings into their daily planning," Ms Golding said.

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