The NSW SES is warning that much-needed rain and thunderstorms forecast to sweep across the state could bring new risks.

Firefighters are hoping the rain will help douse the 88 fires still burning across NSW.

“Some rainfall has started falling across a number of fire grounds. We have everything crossed hoping for some good falls across these areas over the coming days,” the NSW Rural Fire Service tweeted late on Wednesday.

Most of NSW is expected to receive rain from Thursday, except for the west and southwest, with the falls to continue into Monday.

Areas around the South Coast and Southern Tablelands are predicted to receive up to 30mm but the Bureau of Meteorology says the rain will be patchy and exact falls are difficult to predict.

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The NSW SES says this could bring on the risk of flash flooding, falling trees and landslips after fire wiped out trees and growth.

“While the rain is welcomed, heavy rainfall and storms in fire affected areas can lead to dangerous conditions such as a higher risk of flash flooding, falling trees and landslips,” NSW SES assistant commissioner Paul Bailey said.

“In areas impacted by fires where vegetation has been destroyed, water from heavy rainfall can flow into riverbeds and we could see run-off in areas we wouldn’t normally, resulting in flash flooding.

“The NSW SES is also asking residents in fire affected areas to watch for possible landslips as the ground and roads can be damaged, therefore creating a higher risk of a potential slip.”

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The SES warned residents to prepare their properties but trimming overhanging branches, cleaning gutters and pipes, securing loose items in their backyards and not parking under trees or powerlines.

AAP.