"After receiving some rainfall today, Newcastle and Hunter regions will see some heavier rainfall over the weekend and the beginning of next week," the bureau added.

The Hawkesbury and Blue Mountains areas have also been warned of large hailstones and severe thunderstorms, which were detected on the radar near Colo and Colo Heights, on Thursday.

An upper level trough has been moving through eastern parts of NSW and is assisting thunderstorm development in the region.

Parts of the Blue Mountains are set to be affected, with Orange, Bathurst and Katoomba in the storm's firing line.

Residents in upper central NSW are preparing for a battering on Thursday afternoon, after large hailstones, heavy rainfall and damaging winds were forecast.

The bureau issued a severe weather warning for parts of the Hunter, Central Tablelands, North West Slopes and Plains, Central West Slopes and Plains and the Upper West Forecast districts.

Rural areas of NSW will also be hit, with severe weather advice given to Walgett, Coonabarabran Nyngan and surrounding areas.

The State Emergency Service warns that flash flooding due to hail could occur, and insists that residents stay indoors in the effected areas, as well as securing loose items around properties due to forceful winds.

For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.