Queenslanders are being urged to cover up as ultraviolet radiation hits extreme levels across much of the state.

Brisbane is expected to reach a top of 17 on Thursday, more than five times the safe limit.

The Bureau of Meteorology predicts similar extreme levels of 16 and 15 will continue until at least Sunday.

Cancer Council Queensland recommends sun protection for levels of three and above.

Spokesman Katie Clift said the old adage that people have to avoid the sun between 10am and 2pm doesn' apply to the sunshine state.

She said the UV in Queensland hit three by 7.30am.

"It won't be extreme the whole day but people need skin protection pretty much the entire time."

Ms Clift said a lot of people who chose to exercise in the early morning or late afternoon would be caught out.

"They will do significant damage, will get a sunburn or just do damage to their skin that they do not notice," she said.

More than 3600 Queenslanders are diagnosed with melanoma each year.

According to Cancer Council Queensland, the majority of skin cancers are caused by overexposure to UV radiation.

Damage can occur in as little as 10 to 15 minutes during peak periods.

Slightly cooler conditions are expected across the southeast on Thursday, but the relief will be shortlived as a heatwave continues to sweep across the state.

Temperatures of more than 40C are expected in the Wide Bay and Burnett region, north of Brisbane.