The unusually warm and dry winter across much of NSW has prompted the Rural Fire Service to bring forward the official start to the fire season for nine local government areas, including the Blue Mountains.

The Bush Fire Danger Period, which requires people to obtain a permit before lighting a fire, will start on September 1 in 28 local government areas, 19 of which permanently start on that date. Six separate areas already start their season from August.

The areas being brought forward this year are Warrumbungle, Gilgandra, Mid-Western Regional Council, Port Macquarie-Hastings, Mid-Coast, Bathurst, Oberon, Lithgow and Blue Mountains.

"Last week we saw a hint of the conditions the upcoming season may bring, with firefighters responding to 612 bush/grass fires that burnt 21,239 hectares, including three Watch and Act fires that threatened homes in Kempsey, Port Macquarie and Port Stephens," RFS Commissioner Shane Fitzsimmons said in a statement.