Deputy commissioner Gary Worboys says he's disgusted by reports of looting during the bushfires crisis.

"Police and emergency services are at the ready to prevent loss of life, livestock and property, and I am disgusted that anyone would target these vulnerable communities at this time," he said in a statement.

"People in these areas have already lost members of their communities, seen property destroyed and suffered emotional turmoil from the recent fire activity, they do not need the added stress of looters stealing what little they might have left."

Both uniformed and plain-clothes officers will be patrolling bushfire-affected regions, Mr Worboys said.

"With thousands of lives and homes at risk today, I can't comprehend the type of person who'd think it's OK to try and profit or benefit at other people's expense," he said.

"Any reports of criminal acts will be thoroughly investigated."

The deputy commissioner said offenders would be "put before the courts".

Extreme fire danger is forecast for six fire districts in NSW's southeast and the ACT while severe conditions are forecast for Sydney, the Hunter and the central ranges.

Five "no go" zones have been established across broad sections of the South Coast, parts of the alpine region and on Sydney's fire-threatened fringes.

Australian Associated Press