The officer is at the centre of an Ethical Standards Command probe over "on-duty border enforcement" activities, the police service says.

A 20-year-old woman has been fined $4135 for entering Queensland on September 15, in breach of health orders. She is now in hotel quarantine.

Queensland Police Acting Chief Superintendent Rhys Wildman says the allegations are "extremely disappointing" but the detection of alleged illegal crossings shows border operations are rigorous.

"Just because somebody gets across the border doesn't necessarily mean that they get a free ride," he told ABC radio on Wednesday.

"We quite often pick up individuals that do provide a version of events which allows them entry into Queensland based on the information provided to officers on those border checkpoints.

"However once they're in Queensland, further follow up investigations are made. And we have had cases, such as this one, where enforcement action is taken."

Premier Annastacia Palaszczuk said the allegations involving the officer were concerning.

"You want everyone to do the right thing," she said on Wednesday.

Australian Associated Press