The city also experienced its first December day above 40 degrees, breaking a temperature record for a second time this week.

By 10am Sunday, the quality had improved at the three measuring stations but remained at hazardous levels. Civic was at 436, Florey 772 and Monash 688.

At noon on Saturday, the air quality index in Florey was 1370, while Civic and Monash both recorded levels above 1100. More than 200 is considered hazardous, while 100 is the national air quality standard.

At these levels, health authorities advise everyone to avoid all physical activity outdoors. Sensitive groups, including those with lung and heart conditions and pregnant women, should temporarily relocate if possible or remain indoors and keep activity levels low.

The smoke haze in the evening caused play to be suspended at the the Big Bash League match at Manuka Oval.

In January 2003, the index peaked at 650, while the index peaked at 596 last week.

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Jelena Dragila of Forde took her dogs to Lake Burley Griffin on Saturday to cool down, but said air conditions were "horrendous".

"I don't even know what to say. I guess it's really hard, you can't get the dogs out and walk them. You can't go out early in the morning or late in the afternoon, because it's really bad," she said.

Ms Dragila said she took the chance to get out into the water in the middle of the day when the air seemed better.

"We usually walk twice a day [with the dogs] and for the last week we haven't been able to go out. I get up in the morning and train, before training it's too smoky and after training it's too hot," she said.

Bureau of Meteorology senior climatologist Agata Imielska said Canberrans should be prepared for the smoke haze caused by bushfires to thicken during the day.

A cooler southerly change first expected for 2pm would be more likely to come through about 7 or 8pm, she said.

At that time the wind will pick up and gusts will add to the poor air quality.

"With that wind change and the dry, warm wind conditions it is exacerbating bushfire risk and obviously firefighting conditions will be more challenging today especially."

Ms Imielska said it might not be a proper southerly change and tend more from the east. The later change could also see temperatures increase through the day.

"Around Canberra and NSW more broadly the temperatures we're seeing in some parts are approaching record warmest December temperatures," Ms Imielska said.

The forecast is for a top of 41 degrees on Saturday, dropping to 27 degrees on Sunday. Monday has a forecast of 34, 31 degrees on Christmas Day and 32 degrees on Boxing Day.

"Tomorrow once the change moves through in the evening [on Saturday], we'll see temperatures dropping," Ms Imielska said.

At 1.44pm Canberra set a new December temperature record, reaching 40.4 degrees at the airport, before the temperature continued to rise to 41.1 at 3.02pm.

The record had been set on Thursday, when the temperature peaked at 39.3, beating the 1939 record of 39.2 degrees.

Canberra did not record a single day above 40 degrees for 25 years between 1973 and 1998. There were nine days above 40 between 1913 and 2006, and there have been 17 since 2007.

ACT Health public health physician Vanessa Johnston last week told the Sunday Canberra Times people sensitive to smoke should avoid exposure and all people should avoid strenuous outdoor activity.

Masks did provide help if they had a filter rated to capture airborne particulates but needed to have a snug fit.

"These masks are generally not available for children and wouldn't necessarily be suitable for people with beards, for example. It has to be a very tight, clean fit for them to be effective. But it is definitely an option," Dr Johnston said.

with Kimberley Le Lievre