Hot, erratic winds and potentially dry thunderstorms could cause havoc for firefighters across parts of NSW amid extreme fire danger warnings.

A total fire ban has been put in place for six regions in the state’s north and northwest amid forecasts of scorching conditions in some areas.

Extreme fire danger warnings have been issued for the greater Hunter, northern slopes and northwestern regions for Wednesday, while those and three neighbouring areas are subject to total fire bans.

Hot and dry conditions with fresh northeast to northwesterly winds will cause dangerous fire weather conditions, the Bureau of Meteorology said.

Conditions could be exacerbated by a fresh and gusty south-to-southwesterly change moving through during the day and thunderstorms, which are likely to develop across the region.

Grafton in the Northern Rivers region is expected to hit 40C.

A convergence zone was expected along the ranges, the NSW Rural Fire Service said.

“That will create erratic winds which could see fires behave in unpredictable ways and create challenging situations for our firefighters,” RFS operational officer Emilie Koek told AAP on Wednesday.

Residents in extreme fire danger areas should take action to protect their life and property, including having a bushfire survival plan and knowing what to do should fire threaten.

As of Wednesday morning, 69 fires were burning across the state including 20 that were yet to be contained.

Keenly watched fires including a 1400ha blaze on Thunderbolts Way, near Gloucester, a 2000ha fireground at Nymboida and a fire that has scorched 1100ha of national park east of Tenterfield and has the potential to jump Timbarra River on Wednesday.

Investigations continue into several bushfires on the NSW mid-north coast that are believed to be deliberately lit.

A fire that started last Tuesday at Belmore River, about 15km east of Kempsey, burnt through nearly 3000ha of bushland in the Hat Head National Park before being brought under control.

Police, including arson unit officers, are investigating after the fire was deemed to be suspicious.

– AAP