A heatwave with temperatures possibly hitting 35 degrees on Sunday and 36 on Monday is approaching the capital, the Bureau of Meteorology forecast.

Duty forecaster at the Bureau Emily McVeigh said the hot spell would see the warmest days of summer so far, peaking at seven degrees above January's average top temperature.

"A high-pressure system coming from south-east of NSW which will direct quite hot air across ACT, starting with some days reaching 30 and 31 degrees on Friday and Saturday "

"It looks like Sunday things will start to really heat up, with a maximum of 35 degrees, and climb to 36 on Monday before maximum temperatures should decrease again to around 31."

Nights will range from a mild low of 14 degrees to warm 19 degrees over the weekend into the next week.

The warmest day so far this summer reached 34 degrees, while Canberra's hottest day on record hit 41.6 degrees during a sweltering heatwave in January 2013.

There was a chance of a few millimetres of rain from Monday to Wednesday, but "unlikely enough to cool people down" Ms McVeigh said.

The heatwave follows the territory's third hottest year, which also had the hottest June to September period on record.

Calvary Hospital emergency department co-director Matt Luther urged pregnant women, people with chronic health conditions, children and the elderly to ensure they protect themselves from the heat during hot spells.

"These individuals should be particularly wary of hot days and also need to consider how the body cools itself," Mr Luther said.

"So if we have a hot July day, our bodies' sweat will be effective but if we have had a hot and humid day our cooling mechanism through that sweat is not as effective."

Mr Luther reminded people to stay hydrated, wear light-coloured and light-weight clothing, take medications as prescribed and use public spaces to cool off if their homes are without airconditioning.