A truck driver is fighting for life his after falling at least 15 metres when his vehicle rolled over on the approach to Melbourne's Bolte Bridge this morning.
The man underwent surgery after he fell from his cab as it dangled over the side of the elevated roadway following the accident, which happened about 6:30am.
CityLink has confirmed the man, aged in his 20s, fell between 15 and 20 metres.
truck driver fell out of the cabin about 20m onto road below
- ABC reporter Ashlynne McGhee on Twitter
Police believe the truck was travelling southbound in the right-hand lane when a car tried to merge in front of the truck.
They think the driver tried to take evasive action and that caused the truck to jackknife.
Police say he then veered across the lanes and back again, before hitting the lane barriers and coming to rest on top of them.
He fell from his cab and landed in Mark Street below, and was taken to the Royal Melbourne Hospital.
The driver of the car that hit the truck has been taken to the Alfred Hospital with minor injuries.
The accident caused rush hour traffic chaos across the city, and emergency crews are racing to clear the bridge in time for the evening commute.
A crane was brought in to carefully remove the truck seven hours after the drama.
The Melbourne Fire Brigade is using a drone to take photos of the areas of the truck they cannot reach.
An eyewitness, Graham, who called ABC Radio, says the scene is like something out of a Hollywood movie.
"It was a tip truck with a trailer on the back and the cabin part is hanging over the edge," he said.
"There were three or four other cars a bit banged up and mess all over the road."
The half-kilometre Bolte Bridge spans the Yarra River and Victoria Harbour in the Docklands precinct.
VicRoads spokesman Dean Zabrieszach says the accident reduced traffic to gridlock this morning.
"Traffic is completely stationary in that area where we're moving all traffic off the Western Link, the Tullamarine Freeway effectively at Flemington Road," he said.
"The Racecourse Road entry ramp is also closed inbound to Bolte Bridge."
Fire brigade spokesman Peter Eagan says the bridge will be closed for up to six hours before two cranes can be brought in to remove the truck.
"I think it will be closed for the better part of the morning, and as much as I would like to say we would be able to open it, the only problem we've got at the moment is removing that truck," he said.
"The truck still remains on the barrier and until we can get some cranes in here ... then the freeway unfortunately will have to remain closed.
"In my experience these things do take a little while. I know the travelling public of Melbourne and others will not be happy about it but I believe at this stage until we can get an assessment done on the bridge by an engineer, get the cranes in place, I think we're looking at somewhere between four and six hours.
"I'm hoping it will be open for the evening peak. If not I'll be disappointed."