Changing conditions are keeping fire fighters on their toes as they battle dozens of bushfires across New South Wales.

The Rural Fire Service (RFS) has issued a number of 'watch and act' alerts for several major blazes and subsequently downgraded them as conditions on the fire ground changed.

RFS spokeswoman Bridie O'Connor says residents in affected areas should not become complacent but instead monitor fire developments.

"The afternoon is the time when we do see the peak of the temperatures and often the winds do really flare up in the afternoon," she said.

Major fires at Yass, Cooma and Sussex Inlet, in the state's south, continue to cause crews the most concern.

The heatwave conditions that triggered many of the fires earlier this week are expected to return tomorrow, but weaker winds mean the state is unlikely to experience Tuesday's catastrophic fire conditions.

A total fire ban has been declared state-wide.