Massive flames are spreading across heathland as nearly 200 firefighters tackled a "very serious" blaze moving rapidly towards nearby homes.
Strong winds were causing the fire, spanning an area of more than 1,000 square metres, to grow amid fears that neighbouring properties could be at risk.
Emergency crews called to the scene, in Dorset, said the fire was the largest to hit the area in more than 30 years.
Investigations into the cause of the fire are continuing but a spokesman for Dorset Fire and Rescue Service suggested it could have been "malicious".
Some 30 appliances and 11 off-road Land Rovers are currently at the site, in Upton Heath, Poole, where four people have been treated for smoke inhalation.
One firefighter was taken to hospital earlier with "extreme exhaustion" while another suffered burns to his arm. Crews were using multiple beaters, hose reel jets, main lines and compressed air foam to extinguish the fire.
Homes in nearby Beacon Hill Road have been evacuated while properties in Long Meadow Lane are also understood to be under threat.
A spokesman for Dorset Fire and Rescue Service said: "We are carrying out an investigation but we do believe the fire might be malicious. The last fire of his magnitude was in 1976."
Area Commander Keith Bacon said: "Crews are working extremely hard to extinguish this fire but the weather conditions are making this difficult.
"This is a very serious fire and we would encourage anyone in properties surrounding the heath to leave their property if smoke or fire enters their back garden."