A bus driver failed to see five warning signs before he hit the low-clearance Montague Street bridge in South Melbourne in a crash that seriously injured six passengers, a trial has heard.

Prosecutors allege Jack Aston was criminally negligent in failing to take heed of signs alerting drivers of a three-metre clearance ahead, as well as a warning sign on the bridge and a red flashing light triggered by a sensor on the road.

Bus driver Jack Aston outside the Melbourne County Court on Tuesday. Credit:Jason South

Mr Aston was driving the 3.6-metre-high bus for Gold Bus Ballarat on February 22, 2016, when he crashed into the bridge at 56km/h at 10.22am. The impact pushed the top part of the vehicle back to the fifth row of seats, the County Court heard on Tuesday.

Four women and two men, who were passengers while attending a conference at the Melbourne Convention and Exhibition Centre, suffered injuries including head and spinal fractures, broken collarbones and facial lacerations. Mr Aston was also seriously injured.