A lorry driver is in a serious condition in hospital after his vehicle collided with another lorry on the M4 in Berkshire.
The accident, on the westbound carriageway between Chieveley and Hungerford, has caused major delays.
The Highways Agency says it is likely to take until this afternoon for traffic to get back to normal.
Thames Valley Police are appealing for witnesses to the collision, which happened at 2.38am.
No arrests have been made at this stage.
Investigating Officer, Sgt Tony Griffiths of the Joint Operations Roads Policing Unit, said: “We are appealing for anyone who was travelling on the M4 in either direction this morning between the times of 2.30am and 3am near to Junction 13 and 14 of the M4 Westbound to come forward as they may have information to help us with our investigation.
Three fire engines attended along with a heavy rescue unit.
The westbound carriageway remains closed, with severe traffic congestion on both the M4 and A34.
Diversions are in place.
The M4 Westbound Junction 13 to 14 is currently closed following an crash involving two HGV lorries.
All lanes Westbound between junction 13 at Chievely and 14 at Hungerford heading away from London are closed and a diversion is taking motorists off the carriageway at Junction 13.
It is likely to be closed for sometime for recovery. The Eastbound carriageway is currently full open.
The A34 southbound is blocked due to accident before M4 J13 ( Chieveley / Newbury). All traffic is being held just before the M4.
Thames Valley Police is appealing for witnesses after a fatal road traffic collision in Chievely during the early hours.
At 00.45am this morning, officers were called to the A34 exit slip road for Priors Court Road, Chieveley northbound in Berkshire to a collision between a car and a pedestrian.
A blue Renault Clio Estate was travelling up the slip road having just exited the A34 when it was in collision with a pedestrian who was on the slip road.
The pedestrian, a 41-year-old man from Bicester, died at the scene.
The driver and passenger of the vehicle were not injured.
The victim’s next of kin have been informed.
Anyone who witnessed the collision or has any information should call the Serious Collision Investigation Unit via the Thames Valley Police enquiry line 101 quoting URN 60 13/12.
The improvement work will start on the eastbound carriageway on Monday and will continue until Friday when it will switch to the westbound carriageway until 22nd February. It will be carried out each night between 10pm and 6am.
Thames Valley Police have confirmed that the A34 has reopened after closing yesterday evening because of an accident. Workers started repairing the surface of the road at 3 o'clock this morning after a car transporter overturned in Berkshire.
The A34 northbound at East Ilsey is expected to remain shut until at least 6am on Wednesday morning while repairs are made to the central reservation and the road's surface following an accident this afternoon. A car transporter overturned at around 4pm.
The A34 Northbound remains closed with queueing traffic due to emergency repairs and earlier overturned lorry between M4 J13 (Chieveley / Newbury) and High Street (East Ilsley).
A car transporter overturned after a collision with another lorry. The incident damaged the central reservation and the road's surface. The car transporter has now been recovered. Repairs to the road are underway.
Thames Valley Police & Highways Agency say the A34 between Beedon & East ilsey will not reopen until 9pm at the earliest. A car transporter lorry overturned near East Ilsey on the A34 northbound shortly after 4pm this afternoon. Drivers are being advised to avoid the area & use alternative routes.