SEVERE thunderstorms bringing large hailstones, heavy rainfall and damaging winds are expected to hit parts of NSW.

The Bureau of Meteorology (BoM) has issued a severe thunderstorm warning for this afternoon with people in parts of the Hunter, Illawarra, Central Tablelands, Southern Tablelands and South West Slopes to be affected.

The BoM says severe thunderstorms are also likely to produced heavy rainfall that may lead to flash flooding in areas such as Bathurst, Katoomba, Goulburn and Young.

The State Emergency Service (SES) has advised people to keep clear of creeks and storm drains, and to move their car under cover or away from trees.

The weather bureau has not issued a storm warning for the Sydney, but the bureaus radar shows the storm front tracking north and east across the outskirts of the greater metropolitan area.