Organisers of the annual Carols of Hope in Belmore Park are reviewing the event after a thick smoke haze blew into the city.
Wind is blowing the smoke in from the Currowan and Tianjara fires, both in the Shoalhaven, Southern Tablelands RFS operations officer, Lachlan Gilchrist said.
Peter Mylonas said he and co-organisers would very likely hold a shortened event, given the heavy smoke.
"Earlier on it was quite clear so we didn't expect it to come in so thick," he said.
Rather than artists performing twice, they would now only take the stage once. Santa will also make an earlier entry, with presents to be dispersed to every child.
Mr Mylonas said organisers could lose some money on the event, which featured a strong line-up of talent, including the Koi Boys.
He said it was the smallest crowd ever, with some 300 people.
Between 4pm and 5pm, the air quality index hit 1156, according to the Department of Planning, Industry and Environment's data from its Leggett Park monitoring station in Goulburn.
It was the highest in the state out of all the monitored sites. Anything above 200 is considered hazardous. People with asthma and other respiratory conditions should stay indoors and avoid physical activity, health authorities advise.
It followed Friday's peak reading of 2266 across all bushfire days in the past week and a half.
Mr Gilchrist said the Currowan and Tianjara fires had joined and smoke from a significant amount of burnt bushland was blowing west over to Goulburn and beyond.
"It will be very smokey tonight and it will stick around for about half of Sunday when we expect it to blow away," he said.
"People can expect a general haze up until Christmas."
Currently, visibility is very poor in the city.
The RFS has imposed a high fire danger rating for the Southern Ranges for Sunday. Mr Gilchrist hoped milder conditions would enable crews to put containment strategies in place on the Green Wattle Creek fireground and those burning around Braidwood.
Meantime, the Currowan, Cumberton and Tianjara blazes have been upgraded to emergency warning.
Keep up to date on these fires on the live blogs listed above.