The victim died 20 minutes after he was set upon in what police called a "chance happening" at the Cairns Central Shopping Centre.

He was attacked on the ground floor about 8am, before businesses had opened for the day. Another man is in custody.

"Our immediate information is that it appears to be a chance happening. The offender was resolute in what he had intended," Acting Detective Inspector Kev Goan told reporters on Wednesday.

"The laceration is to the throat. He passed approximately 20 minutes after the wounds were inflicted."

The victim, aged between 30 and 40, was known within the shopping centre but police believe his attacker was a stranger to him.

"I can say the gentleman is known within the centre and the dealings he's had with proprietors within the centre has been very positive," Insp Goan said.

"He readily engages with others and is described as a fairly laid-back, easygoing nice gentleman."

He said there were a number of witnesses and CCTV footage would be crucial in piecing together what happened.

The man who's been arrested is 39 years of age.

The centre is now partially open, including its major stores, but some retailers remain closed for now.

Centre manager Christie-Lee Jackson declined to comment when asked if the victim was associated with any particular business.

"We're assisting police with their investigation, and as always the safety of our customers and staff is paramount."

Australian Associated Press