FIREFIGHTERS are frantically working to free four passengers who are trapped in the wreckage of a bus which struck a bridge about 10.40am.
Another 15 people have already been pulled from the tourist bus.
So far, none are thought to have life threatening injuries.
The bus is understood to have been a metre too tall for the Montague St bridge in South Melbourne and hit it without slowing down.
Car salesman Ramsey Melhem told Fairfax said trucks were regularly striking the bridge but the strikes were never this serious.
"I just don't understand how he (the driver) could have hit it, it was pretty obvious that he wasn't going to get through," Mr Melhem said.
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