The mercury is tipped to hit 40 degrees on Thursday and 42 degrees on Saturday.

Heavy smoke haze from NSW bushfires again rolled through Canberra on Tuesday night with periods of haze expected to stick around until at least Saturday.

By 8am Wednesday morning, all air quality stations across Canberra were recording hazardous levels.

ACT Health said the Florey station was recording an index level of 817 - four times the base level considered hazardous.

Monash recorded a level of 581 while Civic's index sat at 546.

ACT's Chief Health Officer Kerry Coleman said Canberrans needed to be prepared for a sweltering summer.

"We're heading into what is actually going to be a hotter, dryer, longer summer - so this is going to be just our first experience of heat," she said.

"It's really important that Canberrans appreciate that this is going to be a long hot summer and very early on start practicing these behaviours around drinking a lot of water ... and staying out of the heat during the middle of the day."

Dr Coleman said the heat plan was only activated twice in the last summer season.

She said the smoke and heat conditions meant Canberrans should be aware of their surroundings.

"Make sure when smoke is around and you're outdoors, don't do any heavy or prolonged activity," she said.

"And for those of us who know we are susceptible to smoke, take those precautions we have been talking about for the last week."

Dr Coleman said people should remember to stay hydrated in the heat, drinking more water than usual.

"Our bodies need more water when they're hot," she said.

"Remember both alcohol and caffeine can dehydrate ourselves. So just balance those festive drinks with intermittent drinks of water."

She suggested going to air conditioned public places like libraries and shopping centres to beat the heat.

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Dr Coleman said heat waves could see more people coming to the territory's emergency departments.

"We hope by doing this messaging and letting them know to anticipate this...then we can reduce those presentations to EDs as well as walk in centres and GPs," she said.

"We really need to be aware of our susceptible and vulnerable in the community during these periods of heat.

"Our babies and our young children, pregnant mums as well as the elderly and people with chronic conditions can feel the heat much sooner and more dramatically."

ACT Health was not yet able to provide any data or anecdotal evidence on whether the long periods of smoke had increased hospital presentations.

"Our message to Canberrans is to really play it smart and to really be aware of what's out there," Dr Coleman said

The next week could see Canberra face its hottest day since records began. A record temperature of 42.2 degrees was set in February 1968, but with Saturday set to top 42 degrees that record could go.