The rating is in place for the Greater Hunter and Greater Sydney regions.

A statewide fire ban is also in place for Monday (November 11) and Tuesday.

Muswellbrook Shire mayor Martin Rush urged residents to avoid bush fire prone areas and to immediately implement their fire safety plans if they have not already done so.

"With the expectation that the weather will worsen on Tuesday, producing catastrophic fire danger conditions for our region, it is critical that people take action now before the risk heightens," he said.

"Council will be working very closely with the NSW Rural Fire Service and NSW Police on a coordinated response to any fire incidents.

"I also encourage residents to report any suspicious activity to police."

Meanwhile, the St Joseph's High School Aberdeen bus from Merriwa will not run on Tuesday.

"This decision was made in consideration of local advice, the school's RFS fire zone rating and the catastrophic fire warning issued," Catholic Diocese of Maitland-Newcastle acting director of catholic schools Gerard Mowbray said.

"In this instance, students - at Abermain, Branxton, Booragul, Bulahdelah, Charlestown, Chisholm, Dungog, Forster, Gloucester, Glendale, Kotara South, Kilaben Bay, Raymond Terrace, Taree, Warners Bay, Windale and Wingham - are not to attend school.

"This advice will be updated daily while conditions remain volatile.

"Safety is our priority.

"Our thoughts and prayers are with our local communities who have been deeply affected by the devastation of these bushfires."

Catastrophic is the highest level of bush fire danger.

Homes are not designed to withstand a fire under these conditions.

If a fire starts and takes hold during catastrophic fire danger conditions, lives and homes will be at risk.

If you are in a life-threatening situation, phone Triple Zero (000).

For fire information, visit www.rfs.nsw.gov.au