Two men were walking near the intersection of Milton Road and Clifton Street before 4am when a man and woman, believed to be in a green Holden Barina, approached.

Police said an argument ensued, which included "lots of yelling" between the man in the car and one of the men on foot.

The dispute ended in the pedestrian being stabbed in the abdomen and back multiple times and the car fleeing the scene.

The 30-year-old German man was resuscitated at the scene by paramedics before being rushed to the Royal Brisbane and Women's Hospital in a critical and unstable condition.

That section of Milton Road was closed for about three hours on Friday, reopening about 7am.

Less than eight hours later the victim was dead and a serious assault investigation became a homicide case.

Detective Superintendent Tony Fleming said CCTV "will prove very important to us".

He added that detectives were continuing to appeal for the man and woman in the car to come forward as well as any other witnesses who could help police to piece together what happened.

He said there was a "significant number of police resources" working on the case and detectives were combing through CCTV footage from the area to try to identify the vehicle involved.

"Today is a tragedy ... it is entirely unacceptable what has happened," Superintendent Fleming said.

Police have taken a statement from the victim's friend who was with him at the time of the attack and the victim's family were in the process of being contacted.

Detectives have set up an investigation centre at the Brisbane City Police Station on Charlotte Street and asked anyone who had further information or dashcam vision to contact Policelink on 131 444 or Crime Stoppers on 1800 333 000.