Two men have been taken to hospital after the vehicles they were driving collided on the Sydney Harbour Bridge.

The ute and car collided head-on about 5.10am (AEDT) on Thursday, blocking lanes on the northern side of the bridge.

Traffic was backed up in the area for about 40 minutes while the men were treated and their vehicles cleared.

The drivers were taken to Royal North Shore Hospital, and police say their condition is unknown.

All lanes on the bridge reopened shortly before 6am.