Councillor Danny Fletcher, of Ashton-on-Makerfield South ward, posted on Facebook and said some of the children had suffered potentially life-changing injuries.
“I’ve spoken with our policing team this afternoon,” he said.
“As we know, three young people have fallen from a top floor side window of a school bus and have been taken to Manchester Children’s Hospital, some with potentially life-changing injuries.
“I’ve contacted the schools involved to ensure they have council support if needed. Sending my thoughts and all my love to the kids and families involved.”
The road has since reopened.
Transport for Greater Manchester said: “Our thoughts are with those injured and we want to wish them a speedy recovery.
“Emergency services remain at the scene, and we are working closely with the bus operator in supporting police with their enquiries into the incident.”