Drivers have been warned to avoid the M4 in Wiltshire with part of the motorway set to remain closed.

Police shut the westbound carriageway of the M4, between junctions 15 and 16 near Swindon, after a serious crash shortly before noon on Saturday, March 9.

National Highways confirmed that the road would remain closed “for some time” while an investigation into the incident is carried out.

Since then, police announced that two lanes have now reopened, with one lane expected to remain closed for hours, causing delays.

National Highways insists the carriageway remains "fully closed."

Air ambulances attended the scene and police say four people were injured after a vehicle left the road and crashed into a tree.

At the time of writing, both National Highways and emergency services teams remained at the scene.

The junction 15 entry slip road heading westbound onto the M4 had also been closed.

Swindon Advertiser: Traffic on the M4 this afternoonTraffic on the M4 this afternoon (Image: National Highways)

National Highways has advised people to avoid the M4 in Wiltshire, if they can, until the road has fully reopened.

A spokesperson said: “The westbound carriageway in this area is expected to remain closed for some time as an investigation is carried out. 

“Motorists are strongly advised to allow extra time to travel, or even delay their journeys if at all possible.

“Further information and updates are available at www.trafficengland.com and travel apps, or via the @HighwaysSWEST 'X' (Twitter) feed.

“Our 24/7 contact centre team is also available to provide up to the minute information on 0300 123 5000.”

In the meantime, those travelling in the area should follow the hollow triangle diversion symbols which have been put in place.

The diversion route can be found in full below.

  • Leave the M4 westbound at junction 15 and take the third exit onto the A419 northbound.
  • Follow the A419 to the roundabout with the A4259 and take the first exit onto the A4259. 
  • Continue on the A4259 until the roundabout with the A4312 and take the first exit onto the A4312. 
  • Proceed on the A4312 to the roundabout with the A4289 and take the third exit onto the A4289.
  • Follow the A4289 to the roundabout with the B4289 and take the first exit onto the B4289 west. 
  • Continue on the B4289 to the roundabout with the B4006 and take the third exit onto the B4006 heading southwest. 
  • Proceed on the B4006 to the Mannington roundabout and take the second exit onto the A3102. 
  • Continue on the A3102 back to the M4 J16 and take the fourth exit to rejoin the M4 westbound.