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 Newcastle, Gosford, Sydney, Wollongong, Canberra, Goulburn and Tamworth.

The Bureau of Meteorology says a trough interacting with a warm and humid tropical air mass in the state's east, ahead of a low pressure system in the southwest of the state, will generate thunderstorms.

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Friday’s warning comes after multiple weather alerts were issued across the region on Thursday. 

Wild weather on Thursday night left about 10,000 homes without power in the Shellharbour area.

Elsewhere, a separate severe weather warning is current for the South Coast.

Persistent moderate rainfall is expected on Friday with heavy bursts of rainfall possible at times, particularly with thunderstorms, the bureau has warned.

Heavy rain which may lead to flash flooding is possible for parts of the South Coast south of about Moruya, including the adjacent ranges.

Rainfall could become particularly intense with any thunderstorm activity, the bureau said.

On Friday, some locations on the South Coast may receive rainfall totals in excess of 150mm. The risk of heavy rainfall may continue into Saturday depending on the development of the low.

A flood watch is also current for the area.

Minor flooding may develop along the Macintyre, Gwydir and Bega Rivers from Saturday.

Local and riverine flooding is possible for the Tuross and Towamba Rivers and local flooding for the Moruya River.