Canberra had its hottest day so far on the day before this in 1979.
The temperature officially reached 37.7 degrees in the afternoon.
And January 7 was even hotter, with a maximum temperature forecast of 38 degrees.
The bureau's temperatures were recorded in the shade and temperatures in the sun were much higher.
One report from Aranda was that the temperature on the grass at 3pm was 43 degrees (108 Fahrenheit).
People sought relief in private and public swimming pools and crowded river swimming spots.
At the Olympic Pool in Civic, for example, about 4000 people crammed in during the day - about three or four times the number on a normal Saturday.
Despite the heat, and the very high fire danger, the ACT Bushfire Council was not called to any fires.
The ACT Fire Brigade attended only two very small grass fires.
"It's most unusual in this heat," a council spokesman said.
"We didn't even have a smoke sighting."
Four fire-observation towers in the ACT were manned all day and the council's helicopter was in the air on patrol.
But the fire brigade was kept busy, checking automatic alarms in buildings which went off because of the heat.
The highest temperature recorded in Canberra is 44 degrees Celsius, on January 4, 2020.