A major incident has been declared as about 100 firefighters tackle a blaze at Holt Heath near Wimborne in Dorset.
The public have been warned to stay away and the fire service said it was trying to protect nearby properties by surrounding the blaze.
Twenty homes have been evacuated as a precaution and locals told to keep windows and doors shut.
Pictures showed smoke billowing into the air from the scene, just north of Bournemouth.
Dorset and Wiltshire Fire and Rescue Service said it was called around 11.30am, adding that the fire was being whipped up by the wind.
“This fire is moving quickly and they [the public] could easily get caught out if they are too close and the fire spreads towards them,” said a statement.
Crews could be at the scene for several days, said a senior firefighter, as hotter temperatures are forecast this week – prompting an amber wildfire alert in the area.
Anthony Bholah, the service’s area manager, said at least 20 engines were involved in the operation and that neighbouring fire services were also helping.
He said the fire covered an area about 1000m by 800m and expected it would be a few days before it’s full extinguished.
“There are some areas that are really difficult to access,” said Mr Bholah.
“So we’re being very cautious about how we approach it and we might call on some additional resources later on this evening.”
It’s not yet confirmed how it started, but he said an investigation would be carried out with police and prosecutions could follow if necessary.
The public has been warned not to fly drones over the fire as they could interfere with firefighters’ own drones.
Read more:
At least two dead as wildfires sweep Greece, Turkey and France
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Crews are also still tackling another fire in Dorset – at Newton Heath, near Swanage – that’s been burning since last Sunday and affects 21 hectares.
That fire is believed to have been started on purpose.
People are being urged to make sure cigarette ends are extinguished properly and to not throw them on the ground or from cars.
Barbeques on heath land, countryside or open spaces should also be avoided, warned the Dorset and Wiltshire service.
Large wildfires burn in Europe
Meanwhile, European nations have been dealing with much more destructive fires in what is becoming a growing problem in the summer.
At least 1,400 firefighters have been deployed in France’s southern Aude region to try to stop the country’s biggest wildfire in decades from reigniting.
The blaze was contained on Thursday after burning through 62 square miles this week.
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Spain is also battling a fire in Avila province, 62 miles west of Madrid.
It had been contained by Saturday afternoon but authorities said the coming hours were critical.
In Greece, flames were fanned by strong winds in the Keratea region on Friday and reached residential areas 25 miles south of Athens.
The same day, smoke also temporarily closed the Dardanelles Strait in northwest Turkey, with a nearby university campus and care home also evacuated.
Local media said the fire started in a field in Canakkale province before spreading to a forested area.
