Lingering smoke from bushfires will again create poor air quality in parts of Sydney on Tuesday.
Air quality reached hazardous levels in parts of southwestern Sydney on Monday evening and was recorded as poor in parts of the city's east.
The state government says air quality on Tuesday will be "poor due to particles" from the extensive smoke coming from bushfires burning across the state.
A temperature inversion forming over the city on Monday night could trap smoke in the Sydney basin on Tuesday, the NSW Rural Fire Service says.
"Smoke levels are expected to be similar if not worse than experienced over recent mornings," the NSWRFS said in a statement.
There were some 125 bush and grass fires burning across NSW on Monday evening with 54 of these uncontained.
There are no total fire bans in place for Tuesday but there is a "very high" fire danger stretching along the NSW coast and in the northern parts of the state.
The out-of-control Currowan fire north of Batemans Bay was burning across more than 16,000 hectares on Monday night, with gusty winds pushing it towards coastal communities.
Firefighters worked throughout Monday night to protect properties from the fast-moving blaze.
The Bureau of Meteorology says smoke is forecast to linger in parts of Sydney into Tuesday.
The heavy smoke blanketing the city is being blown from large bushfires in the Blue Mountains and near Warragamba Dam.
Sydney has been regularly plagued by hazardous air quality levels as bushfires have raged in recent weeks.
A fire burning in the Blue Mountains near Katoomba was downgraded from a watch and act alert level to an advice alert on Monday night.
Firefighters had previously warned residents the 600-hectare fire was spreading towards "built-up areas".
NSW Police have expressed concerns about the number of people deliberately lighting fires.
Two million hectares of NSW land have been burnt since July in more than 7000 fires, with authorities dubbing it the "most challenging bushfire season ever".
Six people have died while 673 homes have been destroyed to date.
Australian Associated Press