Police are continuing to search for a blood-covered intruder who repeatedly stabbed a security guard at an elite Brisbane girls' school.

The man, aged in his 50s, was attacked after he disturbed the prowler at Somerville House in South Brisbane about 5.30am local time.

He was taken to Princess Alexandra Hospital where he is in a stable condition with non-life threatening knife wounds to his torso and arms.

Police remain on scene at the exclusive school as investigators review CCTV footage in a bid to identify the offender.

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Somerville House communications director Sarah Dreaver said the school had an extensive surveillance system comprised of "hundreds of cameras".

"Hopefully that's going to provide them (police) with some assistance in terms of tracking down the offender," she said.

Dreaver said the school was kept open on the advice of police but parents had been kept informed since 7am and students were being offered support.

"It was established that the offender left the scene," she said.

"We consider it to be a really unfortunate, random incident."

Detective Inspector Tony Geary urged members of the public to be vigilant as it was believed the attacker, who fled on foot, may have boarded a commuter train.

"It's certainly likely that the offender has blood on them and it's quite possible that the offender is still armed," he told reporters at the scene.

Initial reports suggest the guard was nearing the end of his shift when he noticed someone trying to break into the school's performing arts complex. The intruder rushed at him and started stabbing when he was challenged.

Dreaver said the guard was a much-loved man. "The school's rallying behind him and his family as we do in the Somerville way," she said.

Somerville House was established in 1899 and is a day and boarding school for girls from prep to year 12, meaning students were on site when the attack occurred. It is also a co-educational school for pre-prep girls and boys.

- AAP