The top deck of the bus had been peeled back as if with a potato peeler

Head teacher Geraint Rees

A spokeswoman for Welsh Ambulance Trust said 22 children were taken to hospital from the scene.

She added that eight were treated for spinal injuries, one for head pains and the others for minor injuries.

It is believed the top of the bus clipped a low-hanging branch of a tree as it passed through Clive Road, Canton, at 0830BST.

The bus, which is registered to a company called EST, was taking children to the Welsh medium schools, Ysgol Plasmawr and Ysgol Glantaf in Cardiff.

All released

Thee road was blocked for several hours while the bus was removed.

Geraint Rees, head teacher of Ysgol Gyfun Gymraeg Plasmawr, said four pupils between the ages of 12 to 15 from his school had suffered whiplash-related injuries - but all were all released and taken home.

Several of the 550 pupils have been helping police with their inquiries into the cause of the accident.

Mr Rees said that, having seen the extent of the damage to the bus, he thought the children were lucky not to have been more seriously injured.

Lucky escape

"The top deck of the bus had been peeled back as if with a potato peeler," said Mr Rees.

"Luckily the bus couldn't have been travelling quickly as the pupils had the chance to move out of the way.

"Had it been a high velocity crash we could have been taking about something very different."

EST Bus Ltd, based in Llandow in south Wales, has been running for 18-months and has had this particular school run contract since January.

Mr Rees said: "They have been a very good company."