United were slated to host Sydney at McKellar Park on Sunday, but the forecast of extremely hazardous air quality has forced W-League officials to reschedule the match.

The club's Y-League match against the Newcastle Jets has also been postponed.

Canberra choked through the worst air quality of any city in the world on Wednesday and Thursday, causing the club to cancel training.

The Emergency Services Agency has declared a "state of alert", with weather conditions set to worsen on Saturday. Temperatures are forecast to reach 42 degrees and the fire danger rating has been increased to extreme.

Canberra coach Heather Garriock is disappointed the match has been postponed but says the most important thing is the players' health and wellbeing.

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"I think it's a smart thing to postpone it, especially if it was going to be played in Canberra," Garriock said.

"Everybody knows in Canberra that McKellar Park is a fortress and it's really important for us to keep it as a home game.

"We're just going to prepare. We haven't been able to train for the last couple of days due to the smoke so I can't wait to get back out on the training pitch and for the girls to have a proper run."

Garriock's side has traveled to Sydney for three training sessions at Football NSW's facilities at Valentine Park this weekend.

United will return to the capital on Sunday night to resume their preparations leading into round nine. The W-League side will face the undefeated Melbourne City in Broadmeadows on Thursday.

"It's been fantastic that Football NSW is available. It's the best case scenario for the team to get a few sessions in, so that way we can prepare for Melbourne City," Garriock said.

"It does [give us more time to prepare] but as a footballer, you always want to play.

"We're disappointed the game has been postponed but in saying that, it's good to have a shorter turnaround. Sydney don't play until next weekend."

The by-product from the surrounding bushfires has also impacted indoor sports facilities across the capital with Basketball Australia opting to cancel a WNBL clash.

The Canberra Capitals were scheduled to host the Perth Lynx at the AIS Arena on Sunday, but the smoke haze has impacted the air quality inside the venue.

Officials hold concerns about the deterioration of the air quality across the city, which could be further intensified by Saturday's forecast heatwave.

The league made the decision to cancel the match on Friday after consultation with AIS Arena and club officials.

The WNBL and clubs involved will engage in further discussions to reschedule the match if the league deems necessary.

"The smoke covering Canberra has been severe and knowing the weather conditions are only expected to worsen this weekend, we trust that this is the best decision for everyone," Capitals manager Lucille Bailie said.

"We hope Canberra will be able to enjoy our game against Perth on another date when the air quality has improved, and we look forward to seeing our supporters at our next home game."

Ticket holders who bought tickets online will automatically be refunded within the next fortnight, while those who purchased through an agency will be contacted directly by Ticketek.

The by-product from the fires raging across the region has forced Tennis ACT to relocate the Canberra International to Bendigo, while an Australian Baseball League series to be played at Narrabundah was also cancelled earlier this week.