The Bureau of Meteorology has issued a new warning for severe thunderstorms, with large areas of NSW to be hit by heavy rain as SES are called to rescue people from rising floodwaters.

The predicted reprieve from rain and flooding across NSW is unlikely to eventuate yet, with only the state's far west expected to be spared from afternoon thunderstorms.

The warning zone includes most of the state - from Mungindi near the Queensland border to Tumbarumba near the Victorian border.