The man, aged about 25, was shot by police outside the Westin Hotel on Mary Street on Sunday morning after reports of a stabbing before 10am.

Police believe two tourists - one male and one female - were walking through the CBD, before being chased by the Brisbane man who was wielding a knife.

While the woman was able to flee, the other man was struck in the face and stabbed in the back.

He suffered a broken nose and a wound to his back.

He was released from the Royal Brisbane Hospital early on Sunday afternoon.

Two officers shot the man dead after he allegedly lunged at them with a knife, according to Detective Superintendent Tony Fleming.

"We don't know the motivation for this attack today," he said.

"It is my understanding that what the police were confronted with today was a life-endangering situation."

Police say there were two knives involved in Sunday morning's incident.

The knife allegedly used to stab the victim was thrown in a rubbish bin around 250 metres from where he was shot by police and he allegedly lunged at officers with a different knife.

Det Supt Fleming said the attacker was known to police and a wide-ranging investigation would take place, including looking at potential terrorism-related motives.

"We do have security and CT (counter terrorism) people with us which will explore that, but I can tell you that at the moment I don't have any information that confirms or makes this an active CT investigation," he said.

Police are appealing for witnesses to come forward with information.

A guest of the Westin Hotel told AAP she heard several gunshots, but thought they were fireworks.

"I came outside and I saw someone lying on the ground and (police) were performing CPR," the guest told AAP.

Investigators from the Ethical Standards Command attended the scene.

Australian Associated Press