An unseasonal spike in respiratory illnesses has hit Queensland, prompting a warning from the chief health officer in the lead up to Christmas.

Across the state there are 322 people hospitalised with COVID-19 - four times the number treated in October.

Another 66 people are in hospital with influenza.

Chief Health Officer John Gerrard said it was unusual Queensland had so many cases in December, urging people to be mindful during the festive season.

"I'm not here to say stop Christmas," he said.

"All I'm saying is if you are sick, try and avoid your elderly and vulnerable relatives and friends."

Dr Gerrard said there had also been a surge in mycoplasma pneumonia, a bacterial infection most commonly occurring in children, with laboratory reports of the illness tripling since November.

"We certainly have not seen significant numbers (of mycoplasma) since before the pandemic," he said.

Mycoplasma infections are usually mild but some children may develop severe complications including brain inflammation or mucositis affecting the eyes, mouth and skin.

"These are rare complications," Dr Gerrard said.

"What we're seeing in hospital is likely to be the tip of the iceberg as to what's actually out there in the community."

He said holiday gatherings, interstate and international travel and the lasting impacts of COVID-19 lockdowns could all have contributed to the spike.

"Two years of the pandemic most of us didn't even get a head cold because the whole world was shut down," he said.

"Probably immunity in the general population against these organisms has waned a little bit because we're not regularly exposed to them now."

Most people in hospital with COVID-19 are over 65 years old and have not had a booster vaccination this year, he said.