Severe thunderstorms may cause heavy rain, flash flooding and damaging winds over large parts of NSW, forecasters warn.
The warnings, issued at 2.06pm (AEDT) on Tuesday are for the central tablelands, parts of the mid-north coast, the Hunter region, northwest slopes and plains, central west slopes and plains and the lower western, upper western and northern tablelands forecast districts.
Thunderstorms are likely to produce heavy rainfall that may lead to flash flooding and damaging winds over the next several hours, the bureau said.
Locations which may be affected include Scone, Orange, Mudgee, Bathurst, Katoomba, Tamworth, Gunnedah, Narrabri, Dubbo, Parkes, Nyngan, Wilcannia and Cobar.
The State Emergency Service (SES) is advising people to move cars under cover and away from trees, secure loose items around dwellings, keep clear of fallen power lines, creeks and storm drains, and to call triple zero if trapped by flash flooding.
People are also being urged to avoid using phones during storms, to unplug computers and appliances and to stay indoors and away from windows.
A strong wind warning has also been issued for NSW coastal waters between Yamba and Crowdy Head.
Winds are north-easterly, then tending southeast to south-westerly and increasing up to 30 knots by Wednesday morning, with combined sea and swell increasing up to three metres.
But the bureau noted that wind gusts could be 40 per cent stronger than the averages given, with maximum waves up to twice the quoted heights.
For emergency help in floods and storms in NSW and the ACT, ring the SES on 132 500.
A spokesman for the NSW State Emergency Service (SES) said about 50 calls for help had been received by 3.30pm.
He told AAP many calls were for minor damage to property caused by high winds.
Calls were fairly widespread but many were from Sydney's northern suburbs and from Bathurst, in the state's west, the spokesman said.
No serious incidents or injuries had been reported.