A green Holden Commodore sedan and a Toyota Yaris were travelling in opposite directions in Crace about 1pm when one of the vehicles apparently crossed into the wrong lane, ACT Policing Sergeant Dick Dauth said.

Police are calling for witnesses, including anyone who may have seen the Commodore involved in other incidents earlier in the day, to come forward.

ACT Policing's crash reconstruction and investigation team were at the site yesterday investigating the circumstances of the accident.

''It's a straight piece of road, and at this time it appears that one vehicle has crossed on to the incorrect side of the road,'' Sergeant Dauth said.

Police, firefighters and ACT Ambulance intensive care paramedics treated the six occupants at the scene. The front passenger of the Commodore, a 29-year-old Ngunnawal man, died at Canberra Hospital a short time after the crash.

The driver of the Commodore and the front passenger of the Yaris were in a critical but stable condition last night.

Three other people, understood to be two passengers from the Commodore and one from the Yaris, were injured but were not in a critical condition.

It is unknown if alcohol or excessive speed were a factor.

''I can't comment on that at the moment, it's early days at the moment.

''We will be investigating it thoroughly,'' Sergeant Dauth said.

The family of the dead man were notified and were at the Canberra Hospital yesterday afternoon.

The fatality takes the death toll so far on ACT roads this year to eight.

Anyone with information should contact Crime Stoppers on 1800333000.