A prison van transferring prisoners has overturned in a road incident.
South Wales Police said the Reliance Security Group vehicle overturned on the A470 by Whitchurch Golf Club in Cardiff at around 1230 BST.
Firefighters helped four people from the van and dealt with a diesel spill.
The ambulance service said "several" casualties would be taken to University Hospital of Wales, Cardiff.
A police investigation has begun.
Officers said the prison van was not the only vehicle involved in the incident near the junction of the M4.
Traffic is being diverted through Rhiwbina.
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