Temperatures began to climb in the ACT on Monday, and will ramp up steadily in the days to follow.

The outlook is for a maximum of 33 degrees on Tuesday, 35 on Boxing Day, 37 on Thursday and an expected 38 on Friday with sunny conditions, very little cloud and mostly light winds. There is little or no chance of rain forecast for the next seven days.

Duty weather bureau forecaster Rob Taggart said that the coming heat wave was likely to be rated severe, and possibly could go higher.

"A high pressure system will sit over this south-eastern part of the continent and stay blocked in place, and this will lead to a steady build-up of temperatures in the next seven days," he said.

"There won't be much relief from the heat at night at night, either. The light winds associated with this system mean that the temperature will continue to build, one day after another."

He said Christmas Eve temperatures were similar to last year, when they peaked at 34.8 degrees at Canberra Airport.

"But last year a cool change then swept through on Christmas Day and dropped the temperature back down to a very comfortable 23 degrees. That certainly won't be happening this year."

He said the earliest possible chance of any relief from the scorching heat on the way might be about New Year's Eve "but it's too early to say with any certainty".

Fire authorities will be watching their indicators closely as the mercury rises but there are no predictions yet of when fire restrictions will be put in place.

The recent rain across the ACT has given some relief from the natural fuels in our forests drying out quickly in the heat to come, and winds conditions will be generally favourable.

A spokesman for ACT Emergency Services said it was too early to make predictions about potential fire ratings for the coming week because the agency uses the latest available data in making its assessments.

However, sustained periods of very hot weather would systematically trigger a range of public health and fire warnings.