Another day of poor air quality for Sydney

There were 69 bush and grass fires burning across the state on Friday afternoon with 40 still to be contained.

Crews undertook backburning across a number of firegrounds in the mid-coast area, the Rural Fire Service said, adding "winds are expected to increase which could challenge containment lines".

A watch and act alert which was issued for a bushfire in Cooperabung, northeast of Port Macquarie, was downgraded on Friday evening to advice level.

The NSW environment department is forecasting air quality in Sydney will be "poor" on Saturday due to particles and ozone.

"(It will be) unhealthy for sensitive people, and could cause symptoms, especially in people with heart or lung disease," the department said in a health message.

The persistent smoke haze resulted in "hazardous" air quality in parts of Newcastle as well as Orange, Wagga Wagga and Muswellbrook on Friday evening.

The air quality was rated as "very poor" in Richmond, St Mary's and Bargo in Sydney, as well as in Singleton.

NSW Ambulance officers have responded to two asthma or respiratory-related call-outs each hour since Wednesday.

The Bureau of Meteorology says the haze is likely to continue as winds from the north and northeast continue to push the smoke south.

"We're expecting the smoke to continue into Saturday and for the first part of Sunday but as showers start to increase about eastern parts, the showers and rain should mix with the smoke particulates in the air and help to reduce the smoke in general," BOM meteorologist Katarina Kovacevic said in a statement.

"During Monday, we're expecting a southerly change to sweep along the coast and those southerly winds should help to clear out the smoke."

Ms Kovacevic said due to the "hit and miss" nature of thunderstorms, they would be unlikely to have a "significant" impact on the firegrounds.

The RFS said some areas across NSW were predicted to receive up to 50 millimetres of rain over the weekend.

"Although this won't put out all the fires and isn't drought-breaking, we will certainly take what we can get," the agency posted on Twitter.

While there are no total fire bans in place for Saturday, the ACT and parts of the NSW will be under "very high" fire danger.

This includes the greater Hunter, Illawarra/Shoalhaven, far South Coast, Monaro alpine, Southern Ranges, Central Ranges, Northern Slopes, north western and eastern Riverina fire areas.

Much of the rest of the state will be under "high" fire danger.

Australian Associated Press