Police say the 38-year-old man's motorcycle collided with a Nissan 4WD car at the intersection of Southern Cross Drive and Ratcliffe Crescent about 5.10pm.

ACT Policing is still investigating the cause of the crash, with Detective Superintendent Mick Calatzis saying he would not speculate on whether speed played a part, or which direction the car and the motorcycle were travelling.

Detective Superintendent Calatzis described the victim as a "family man".

McGregor man Peter Voelker was one of "dozens" of witnesses who rushed to help the victim, many performing CPR on the man before paramedics arrived.

"It was awful, I'm still shook up about it," Mr Voelker. "I just wish we could have saved him.

"Our condolences and respect go out to the family, it's obviously a very challenging time for them as well and we have a lot of empathy for them," Detective Superintendent Calatzis said.

There was one man in the 4WD, who was not injured and is assisting police.

The accident is a coronial matter, Detective Superintendent Calatzis said.

It is the second fatality on ACT roads this year.

In January a man died in a single-vehicle crash on Yarra Glen in Hughes.

"We want to go to zero vision, this is one fatality too many in the ACT, this is our second one for the year," Detective Superintendent Calatzis said.

"We want to keep our roads safe, we want to keep Canberra safe, and everybody who drives on the road, we want to make sure they take their fair share of responsibility."

Earlier on Thursday, a minor was taken to hospital after the unregistered motorcycle he was riding collided with a ute in Fyshwick.

Mr Voelker said he thought all drivers should receive education on how to best respond to a car crash.

"You need to know what to do if you drive by and see that, what to look for, if you need to apply a tourniquet or whatever else," he said.

While there are witnesses, police are asking anyone with information to contact Crime Stoppers on 1800 333 000.

with Sherryn Groch