The Sydney region could be in for a stormy evening with thunderstorms possible well into the night, with soaking rain to follow on Tuesday, forecasters said.

The Bureau of Meteorology on Monday issued a severe thunderstorm warning for large hailstones and damaging winds for people in the Blue Mountains and Hawkesbury regions.

A separate warning has also been issued by the bureau for severe thunderstorms including hail, heavy rain and destructive winds covering much of the northern and central parts of the state.

The region covered by this alert includes Mungindi, Moree, Wee Waa, Narrabri and Baradine, and is in effect "for the next several hours", the bureau said.