In the wake of Saturday's bridge collapse in the city's north, the CFMEU is planning a crack down on of safety audits on construction jobs around Canberra, starting this morning.

The half-built bridge, part of the Gungahlin Drive Extension project, collapsed on Saturday during a concrete pour, injuring 15 workers with nine of them being treated in hospital.

CFMEU ACT branch secretary Dean Hall said, ''They heard a crack, there was a three-second delay and then it gave way.''

Dean Hall said on Sunday that the formwork contractor at the Gungahlin Drive job was also working on the Russell roundabout project and union officials planned to be auditing safety systems at the Russell site by 8am today.

''We are going to focus on the Russell flyover because that is the same formworker who is doing the Barton Highway one,'' Hall said.

''We don't know what caused the collapse at this early stage but it makes sense to examine all formwork going on in the ACT, particularly concentrating on where that contractor has been doing work to make sure there are no systemic failures in their systems.''

CFMEU ACT had reported the contractor, Rayners Construction, to work safety authorities, alleging that ''sham contractors'' were being used on the site.

Work Safety Commissioner Mark McCabe was unable to confirm whether Rayners had been audited. The company could not be contacted for comment on Sunday.

Authorities are braced for traffic turmoil in Canberra's north with the Barton Highway likely to be closed for at least two weeks. Roads ACT are urging Northside residents to avoid the area where possible.

Those taken to hospital had injuries ranging from broken arms and legs to suspected spinal injuries.

Two of the injured men remain in a stable condition in Canberra Hospital and CFMEU ACT alleges that the men may not be covered for workers' compensation.