A crash involving a military vehicle has closed a dual carriageway in both directions, trapping drivers in queues for several hours.
Emergency services were called to the A34 on the Berkshire-Hampshire border, near Newbury, at about 11:00 BST.
An air ambulance was due to land at the scene of the “serious collision”, National Highways reported.
Witness Charlotte Aggett said one military vehicle, which was travelling in a convoy, overturned while another one crossed the central reservation.
She posted on Facebook: “About 12 minutes ago we witnessed a large crash as the A343 merges with the A34.
“Four military vehicles were convoying very close together and as vehicles trying to join the road one of the military vehicles flipped as it turned and rolled twice.
“Another of the convoys went over the central reservation trying to avoid the collision, causing another collision on the other side of the road.”
National Highways said the A34 was “likely to remain closed for several hours” between the A343 and the A4.
Hampshire police said: “We were called at 11.04am today to a report of a multi-vehicle road traffic collision on the A34 near Wash Water.
“A man in his 20s has suffered a serious injury to his leg and has been taken to hospital.”
