Police in Greater Manchester are appealing for witnesses after the roof was ripped from a doubledecker bus when it hit a low-level aqueduct.

The incident happened at about 3pm on Monday, when the number 100 Bee Network bus struck the Bridgewater canal aqueduct on Barton Lane in Eccles.

It is believed that the bus had come off its expected route, police said, adding that the driver had failed to comply with height restriction warnings, including hanging chains and signage.

The top level of the bus was torn off in the collision, and a member of the public was ejected from the upper deck. Three people – a 19-year-old woman and two men, one in his 20s and another in his 40s – sustained serious injuries and remain in hospital in a stable condition.

Another 17 people were treated at the scene for injuries that were described by police as not being life-threatening or life-changing.

The driver of the bus, a man in his 50s, was arrested on suspicion of causing serious injury by careless driving and has since been bailed pending further investigations.

Police are appealing for witnesses to come forward, as well as for members of the public to supply any footage, including dashcam, mobile phone or doorbell footage, from the area in the moments leading up to the collision.

Transport for Greater Manchester said its “absolute focus has been on supporting emergency services in their response”.

“An immediate and urgent investigation into the circumstances is under way and we are working closely with the investigation team at Greater Manchester police and the bus operator, Stagecoach,” said Vernon Everitt, the transport commissioner for Greater Manchester.

“This is clearly a distressing situation for everyone involved and we’d like to thank emergency services for their swift response.”