UPDATE: 2.26am

A Welsh Government spokeswoman has confirmed that the road reopened at 12.50pm.

All westbound traffic had previously been diverted along the A48.

UPDATE: 12.36am

A spokesman for the Welsh Government said the road is due to reopen at 2pm, following a clean-up from the highways authority.

The fuel leak which has closed the M4 involves 400 litres of diesel.

A spokeswoman from South Wales Fire and Rescue service said that crews from Duffryn, Treharris and Roath were in attendance and stopped the leak, before leaving the scene at 10.20am.

THE M4 is closed westbound due to a fuel spillage between J29 A48(M) and J30 at Cardiff Gate.

UPDATE: 10.19am

Heavy traffic is reported as emergency service deal with the broken down lorry which is spilling fuel on the carriageway just before J30.

The carriageway has been closed for safety.

Cameras show traffic is heavy on the approach to the closure and on the diversionary route.

Diversion: Via A48 (M) and A48 to Pontprennau then A4232 to rejoin the motorway at J30.