The Bureau of meteorology has issued a severe thunderstorm warning for people in the Illawarra, Central Tablelands and parts of the Hunter, Metropolitan, Southern Tablelands and North West Slopes and Plains Forecast Districts.

Severe thunderstorms are likely to produce 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 Penrith, Wollongong, Bowral, Mudgee, Bathurst and Katoomba. 

The State Emergency Service advises that people should: 

* Move your car under cover or away from trees. 

* Secure or put away loose items around your house, yard and balcony. 

* Keep clear of fallen power lines. 

* 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 8:15 pm.

If severe thunderstorms develop in Sydney, Newcastle, Wollongong or surrounding areas, a more detailed Severe Thunderstorm Warning will be issued to people in this area.

Warnings are also available through TV and Radio broadcasts, the Bureau's website at www.bom.gov.au or call 1300 659 218. The Bureau and State Emergency Service would appreciate warnings being broadcast regularly.