AN UPDATED severe thunderstorm warning has been issued for parts of NSW, though the warning for Sydney's metropolitan area has been cancelled.

The latest warning, issued at 5.37pm, was for peoplein the Hunter, Central Tablelands and parts of the Mid North Coast, Central West Slopes and Plains and South West Slopes Forecast Districts.

Severe thunderstorms are likely to produce large hailstones, heavy rainfall that may lead to flash flooding and damaging winds in the warning area over the next several hours.

Locations which may be affected include Newcastle, Gosford, Orange, Mudgee, Bathurst, Katoomba, Dubbo, Parkes and Cobar.

Earlier, a warning was issued for a large swathe of NSW including Coffs Harbour through to south of Sydney.

The warning was issued for  people in parts of the Maitland/Cessnock, Greater Newcastle and Gosford/Wyong areas.

The Bureau of Meteorology warns that, at 4:15 pm, severe thunderstorms were detected on weather radar near Wyong and Warnervale.

These thunderstorms are moving towards the east. They are forecast to affect Toukley, Tuggerah Lake, Cessnock and Gorokan by 4:45 pm and Budgewoi, Maitland, Kurri Kurri and Bolwarra by 5:15 pm.

Heavy rainfall that may lead to flash flooding and large hailstones are likely.

Thunderstorms across the afternoon have been producing heavy rainfall for up to 30 mins and small hail ( less than 2cm.)

KEEP UP TO DATE WITH THE LATEST WARNINGS HERE

The State Emergency Service advises that people should:

* Move your car under cover.
* Keep clear of creeks and storm drains.
* Don't walk, ride your bike or drive through flood water.
* If you are trapped by flash flooding, seek refuge in the highest available place and ring 000 if you need rescue.
* Unplug computers and appliances.
* Avoid using the phone during the storm.
* Stay indoors away from windows, and keep children and pets indoors as well.
* For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.

The next warning is due to be issued by 5:25 pm.

A more general severe thunderstorm warning is also current for the Mid North Coast, Hunter, Metropolitan, Central Tablelands and parts of the Illawarra, Central West Slopes and Plains, South West Slopes and Lower Western districts.