A large fire has broken out next to the M25, forcing a section of the motorway to close as firefighters tackle the blaze.
Emergency services are at the scene in St Albans after the fire started at an industrial estate in Ventura Park at around 9.21am.
Pictures on social media and released by National Highways show thick dark smoke rising above the carriageways, with road closures in place.
Commuters have been warned that there are currently delays of around 60 minutes in both directions as a result of the fire.
Due to the risk of secondary explosions, along with smoke and debris affecting the carriageway, the motorway remains closed as a precaution, National Highways said.
Given the incident’s proximity to a railway line, Network Rail have confirmed they are also at the scene liaising with fire fighters.
Drivers have been advised "to allow significant extra time for their journeys and consider alternative routes".
A Hertfordshire Fire and Rescue Service spokesperson 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.”
Deputy Chief Fire Officer Mark Barber said firefighters are "working hard to bring the situation under control".
He said: "Fire Control has received a significant number of calls regarding this incident, and I would like to reassure residents that firefighters are working hard to bring the situation under control."
Firefighters have been battling a series of fires across the UK, including one in the New Forest National Park, Hampshire.
Hampshire and Isle of Wight Fire and Rescue Service said on Tuesday that crews had worked through the night, battling a challenging change in wind direction, and were managing to contain the fire, which started after a van caught fire on the A31 near Ringwood on Sunday.
The area hit by the blaze is protected heathland and home to a number of rare species, according to the New Forest National Park Authority.
South Wales Fire and Rescue Service said on Monday night that crews were attending “multiple wildfire incidents”, including at Cwmavon Woods in Blaenavon, Wattsville in Sirhowy Valley and Abernant in Aberdare.
Firefighters have warned they need more funding as they face increasing pressure from “an unprecedented summer of dangerous and volatile wildfires.”
As three quarters of England was plunged into drought on Monday, the Fire Brigades Union (FBU) has said crews across the country would need access to the best equipment as the consequences of climate change become a “national priority”.
On Tuesday, an amber warning for extreme heat has been issued by the Met Office for Thursday, as some parts of England face temperatures of up to 38C.
The forecaster has issued the warning for London and parts of the South East, East Midlands, East of England, West Midlands and South Yorkshire from 9am to midnight on Thursday as temperatures are to climb to 37C or 38C in some places.
The Met Office says that after a warm night, a spell of “very hot weather” will affect England on Thursday, with the highest temperatures in parts of the East, South East and Midlands, potentially affecting transport, infrastructure and health.
Met Office chief forecaster Chris Bulmer said: “While the peak heat will be more short-lived than recent heatwaves, temperatures widely into the mid-30s Celsius on Thursday brings the potential for impacts for some, which is why a Met Office warning has been issued.
“High pressure is now becoming dominant and temperatures will build day-by-day. Southerly and south-easterly winds will also tap into the hot conditions over Europe which helps develop this further notable heat in what has been a hot and dry summer so far for many in the south of the UK.”
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