UPDATE 6.32pm: Eastbound queues have now largely cleared but westbound, traffic remains heavy and slow-moving for several miles between junctions 25a (A4042, Newport) and 23a (Magor services).

The crash which blocked two lanes of the M4 eastbound between junctions 25a and 25 (Caerleon) late this afternoon has been cleared, and all lanes are now open. 

UPDATE 5.14pm: Traffic is tailed back eastbound to shortly before junction 30 (Cardiff Gate), but on the A48M eastbound, the queue stretches back to the junction for the A4232 linking to the Cardiff docks road and Cardiff Road.

Westbound on the M4, traffic currentlystretches back several miles from junction 25, to the area where of the toll booth used to be.

UPDATE 5.04pm: Congestion is as far back as to Cardiff. Eastbound seems to be particularly congested.

UPDATE 5pm: All the lanes have now re-opened.

UPDATE 4.25pm: Traffic is now tailing back several miles eastbound from junction 25 (Caerleon), towards junction 30 (Cardiff Gate), and also westbound, from junction 25 to beyond junction 23a (Magor services).

The outside lane is now closed eastbound at junction 25a (A4042, Newport) while emergency services deal with the crash.

Previously, the middle and inside lanes were closed here, but these have now reopened.

UPDATE 4.14pm: Travel time eastbound from junction 29 (A48M) to junction 25 (Caerleon is currently estimated at 45 minutes. 

A CRASH has caused five miles of traffic and two lanes to close on the M4.

The incident happened on the M4 Eastbound from J25A A4042 (Caerleon) to J25 B4596 (Caerleon).

There is now congestion as far back as to J29. 

Travel time is currently 25 minutes.

More to follow soon.