Police say the driver of the minibus lost control following a suspected blown tyre. The minibus, which had been travelling in the fast lane, crossed the carriageway and left the road where it overturned, throwing at least two passengers from the vehicle in the process.
The northbound carriageway was initially closed to allow Helimed access to the scene. However air ambulances landed in a nearby field where the three seriously injured people were collected and flown to Southampton General Hospital where they remain in a life-threatening condition.
Seven other people – including two children – were walking wounded. They have been taken to Southampton General Hospital to be examined.
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The A27 will remain closed in both directions near Lewes during rush hour due to a large fire at a recycling plant.
Friday morning's forecast for the east of the region
Friday morning's forecast for the west of the region