A huge fire closed a stretched of the M25 in both directions amid fears of “secondary explosions”.
Motorists were halted between J22 (St Albans) and J21A due to the “significant” fire close to the motorway, according to National Highways.
It warned: "Due to the risk of secondary explosions, smoke and debris affecting the carriageway, the motorway has been closed in both directions as a precaution."
Hertfordshire Fire and Rescue Service said: "We are currently responding to an incident in Ventura Park, Old Parkbury Lane, Colney Street, St Albans.
"If you live locally, we advise to keep doors and windows closed and please avoid the area while emergency crews carry out their work."
In an update early on Tuesday afternoon, National Highways said the motorway had reopened on the advice of firefighters, although motorists still faced long delays.
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Fire chief speaks following explosion
A fire chief has said that it will be “several hours” until the fire is extinguished following an explosion close to the M25 earlier today.
Deputy chief fire officer Mark Barber said: "I would like to reassure residents that firefighters are working hard to bring the situation under control."
He said ten fire engines remained at the scene on Monday afternoon and crews had "successfully contained the fire within the unit".
"Crews are continuing to tackle the fire, but we expect it to be several hours before it is extinguished."
He also thanked the public for their patience and understanding.
Details following M25 chaos
The M25 closed due to the risk of a "secondary explosion, along with smoke and debris affecting the carriageway" earlier today, with 15 crews at the scene.
The motorway was shut for around one hour, later reopening with 40mph speed restrictions.
The explosion took place at Malibu Sun, a sun protection company which was founded in 1999.
People were asked to keep their doors and windows closed and to avoid the area, and there were also road closures in St Albans, at Colney Street and Old Parkbury Lane.
Congestion remains despite lanes reopening
All lanes have reopened on the M25 anticlockwise between J13 and J12 near Staines following an earlier traffic collision.
According to the latest update from National Highways, there are currently delays of around 90 mins on the approach, and approximately 5 miles of congestion.
M25 reopens but delays of over 40 minutes remain
The M25 has re-opened but delays of more than 40 minutes remain, National Highways said.
There are 40 mph speed restrictions following instructions from fire crews, and "due to the volume of traffic, it may take time for congestion to clear."
Strong smell of 'burning timber and plastic'
While smoke continues to billow above the industrial estate, the Herts Adviser is reporting a strong smell of “burning timber and plastic” filling the local area.
The fire is now contained, but is still ablaze.
It is still unclear at which unit the fire took place.
Local road closures remain in place
Herts Police has confirmed that local road closures are still in place as a result of the fire.
There are closures between Radlett Lane and Old Parkbury Lane, as well as between Smug Oak Lane and the Premier Inn Hotel.
Motorists are being asked to avoid these roads until further notice.
Meanwhile, the M25 is open in both directions though speed restrictions remain in place.
Fire could take several hours to extinguish
The fire could take several hours to extinguish, the Hertfordshire Fire and Rescue Service has said.
In a statement, Deputy Chief Fire Officer Mark Barber said: “Our firefighters have been working alongside colleagues from London Fire Brigade to bring the fire under control, and have successfully contained the fire within the unit.
“Crews are continuing to tackle the fire, but we expect it to be several hours before it is extinguished.”
Smoke rises from a fire on an industrial estate close to the M25 motorway in St AlbansPABlaze contained but still burning
The blaze at an industrial unit near St Albans is now contained, The Standard understands.
However, the fire at one of the units in the park is still ablaze with fire crews still working to extinguish it.
Dramatic footage shows warehouse fire
Scenes from earlier today show the warehouse fire billowing smoke across local homes in Hertfordshire.
Some wrote on social media that smoke could be seen from Potters Bar and from Bushey, while others reported seeing smoke from the other side of the M25.
It is unclear whether the fire is under control.
Smoke now clearing over the M25
Live camera footage shows that smoke above the M25 is now beginning to clear as crews continue to tackle the fire.
Smoke has stopped billowing across the motorwayNational HighwaysLatest updatesOlder updates