Flood-impacted communities across NSW are being warned to brace for another soaking over the weekend, as thunderstorms begin creeping through the state.

The State Emergency Service is already undertaking one of the biggest resupply missions in its history, bringing groceries, medicine and fodder to cut-off towns.

Urgent supplies are being dropped to isolated communities, including Walgett, Collarenebri and Lightning Ridge in the state’s north.

The agency has fulfilled 893 requests for resupply since the flooding event began in September.

The Bureau of Meteorology is now warning large swathes of the state are likely to be hit with thunderstorms ahead of heavy rain on Sunday.

“We’re now looking at a slightly broader area where we may see some severe thunderstorm development,” BOM meteorologist Helen Reid told AAP on Thursday.

She said western parts of the state could experience severe thunderstorms, but more of the north could also be impacted.

“With all the flooding around, it might not take much of a thunderstorm to be a problem for flooding,” Ms Reid said.

Storms were already battering the far west of the state on Thursday, and will travel further east on Friday.

Weather authorities are likely to issue flood warnings as early as Friday ahead of expected weekend downpours.

The SES is monitoring forecasts and expanded its focus to flooded towns along major river systems across the state.

“Unsettled conditions are expected as the week goes on, which brings a high risk of severe storms,” the SES said in a statement on Thursday.

Authorities are urging people along the Murrumbidgee River, including Narrandera, Darlington Point, Hay and Wagga Wagga, to prepare and check for road closures, with many already flooded.

Emergency services are also carrying out damage assessments in the flood-impacted towns of Forbes and Condobolin along the Lachlan River.

The SES responded to 217 calls for help in the 24 hours to Thursday afternoon, including two flood rescues. There are 91 warnings in place across the state, with 11 at emergency level.

Meanwhile, insurance companies have finalised more than 236,400 claims stemming from floods in southeast Queensland and northern NSW this year.

The cost of those floods has now reached $5.56 billion, making it Australia’s equal most costly natural disaster.

– AAP