Image source, National HighwaysImage caption, The smoke billows across the M25 near St Albans
The risk of an explosion at a large warehouse fire has closed both carriageways of the M25 between junctions 22 and 21A.
Hertfordshire Fire and Rescue was called to the blaze in Ventura Park, Old Parkbury Lane, Colney Street, in St Albans, at 09:21 BST.
National Highways said the motorway was shut, 15 crews were at the scene and there was a risk of a "secondary explosion, along with smoke and debris affecting the carriageway".
People have been asked to keep their doors and windows closed and to avoid the area.
Hertfordshire Police confirmed the M25 closure was due "to smoke from a warehouse fire".
It said there were also road closures in St Albans, at Colney Street and Old Parkbury Lane.
National Highways said because the warehouse was close to the railway line, Network Rail had a representative on site liaising with the fire service.
There are delays of about 60 minutes in both directions on the approach to the closed section.
Drivers have been advised "to allow significant extra time for their journeys and consider alternative routes".
The fire service said it had "received a significant number of calls regarding this incident".
A spokesperson added that firefighters were "working hard to bring the situation under control".
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