Emergency services were called to Highleigh Road in Sidlesham, near Chichester, at about 8.20 today following reports of a bus in a ditch.
The driver of the bus has been treated at the scene and the injured children required no further hospital treatment, according to South East Coast Ambulance Service.
Police have now begun looking into the circumstances of the collision.
A spokesman for Sussex Police said: "Emergency services were called to reports of a school bus having been involved in a collision in Highleigh Road, Sidlesham, at around 8.20am on Monday (February 7).
"All occupants of the bus, which includes a number of schoolchildren and the driver, have been safely evacuated.
"The driver was treated at the scene by the ambulance service for minor injuries and a number of children are understood to have suffered minor injuries.
"The road has been closed in both directions and enquiries are ongoing into the full circumstances of the incident."
Business owner Chris Pink had been driving his little boy to school when he came across the bus.
Chris said students appeared to be 'a bit shocked' following the incident which saw the bus driver and a number of students escape with minor injuries.
He added: "The sun was so bright everyone was going really slowly and then we drove round the bend and saw it.
"We drove past and my boy said 'there's people in there Dad, you need to do something'."
Chris first called The Selsey Academy to let the school know what had happened.
The bus driver was stood at the door helping the children off the bus while Chris made sure the students stayed off the road.
"The kids were walking around in the road so I corralled them into the driveway of a cottage so they knew they were being looked after," he added.
"It was about trying to keep the kids all in one spot. It's nothing really but sometimes you need someone to be vocal - I just wanted to try and help out.
"There were a couple of girls who were shaken up but it is just one of those things. Everyone seemed good. The driver was a little bit shocked."
Stagecoach has said it is liaising with West Sussex County Council and are supporting police with their enquiries..
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Emergency services attended the incident this morning. Picture Eddie Mitchell
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Emergency services attended the incident this morning. Picture Eddie Mitchell
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Emergency services attended the incident this morning. Picture Eddie Mitchell
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Emergency services attended the incident this morning. Picture Eddie Mitchell