Drivers are being advised that a section of the eastbound carriageway of the M4 at Swindon is totally closed and two lanes of the westbound carriageway are also closed.
Wiltshire Police is investigating after a serious collision between junction 15 and junction 14 shortly after midnight.
The collision, involving a car, a van and a partially-laden car transporter, happened at about 12.20am just over a mile east of junction 15 and resulted in several serious injuries. Drivers are advised to avoid the area if at all possible.
A diversion between junction 15 and 14 is in place for eastbound traffic. The signed diversion is advising drivers leaving the motorway at junction 15 to follow the 'hollow circle' diversion symbol via A419 north towards Swindon, B4192 eastbound towards Hungerford then the A338 to rejoin the M4.
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