It is believed the truck is carrying chemicals and police have sealed off the area.
The accident happened shortly after 11am.
Ambulance crews have taken some casulaties to hospital.
Police said a crane had struck the large concrete pedestrian walkway which crosses the highway near Devonshire Street, between Maitland park and the railway station.
Early reports suggested several people may have been injured, but police are still completing their search.
The bridge has landed on the highway, blocking both lanes of the highway and causing traffic chaos.
Police have set up road blocks as ambulance, fire rescue and hazmat units race to the scene.
A command centre has been set up west of the accident.
As the enormity of the situation sinks in police called for structural engineers to come to the scene to assist with shoring up the remainder of the damaged structure.
There were also fears that the bridge may have been "live'' as it brought down power lines and emergency crews from EnergyAustralia have been called in to assist.
More than 30 police from Maitland, Morpeth and Kurri Kurri are on scene assisting with the search and setting up traffic control.
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Updated news is that a cherry picker hit the bridge, it collapsed and landed on 2 trucks and a car... no one was on the bridge which is a mircale, since it is a busy bridge. There was a swimming carnival on accross the road and hundreds of kids had used that bridge to get there only a little earlier.
This was a couple of minutes from my house O_o
have never had any news like this happen near me before...
Bet With routsounmanman: By the end of Q1 2008 Capcom WONT have announced a RE5 Wii Edition OR a new RE (classic gameplay) for the Wii (WON)
