Drivers are facing long delays on the M1 in Hertfordshire and Bedfordshire after a lorry carrying chemicals caught fire.
Both carriageways of the motorway were shut after the lorry suffered a blow-out and caught fire between junctions 9 and 10, the Redbourne and Luton airport turns.
The northbound carriageway is closed between junctions 8 and 9, and the southbound between 10 and 11.
The police and fire service are attending the scene.
Hertfordshire Police said queues have been building up on the motorway, with a knock-on effect on the M25 where there are also long tailbacks.
It is not thought the chemicals the lorry was carrying were toxic.
No-one was hurt in the incident.