UPDATED WITH VIDEO: Hunt for arsonists after major fire on Canford Heath

Dorset Fire and Rescue service estimated the blaze covered up to  seven hectares of heathland – the size of 10 football pitches.

Nine fire engines, fire Land Rovers and an off-road water bowser were on the scene.

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Conservationists say the fire destroyed a Dartford warbler's nesting site. They are already predicting the area could take 15-20 years to recover.

Dorset Fire officers were still on site this morning damping down the scorched earth.

A crew member said some areas of the ground were still “red hot” as he was spraying water on them.

The scorched heathland continued to give off steam as water was put on it and the incident was kept 'open' until around 10am as the situation was monitored.

A large area was left blackened, along with two smaller separate areas, which lay on the other side of an access track used by dog walkers, joggers and cyclists.

One woman who had seen the flames on Tuesday night was walking the area early yesterday morning to assess the damage.

The resident, who lives nearby and asked not to be named, said: “I heard the helicopter and some of my neighbours did too.

“I thought 'please don't let the whole heath be on fire', as it's a tinderbox at the moment. People will do it, they're just destructive.

“Thank God it was just this patch, they did a marvellous job. My first thought was all of the animals as it's a special place up here.”

The fire crew carefully examined the scene, doing a loop around it, to check for any remaining hot spots before leaving.

Station manager Julian Lockwood said at the height of the blaze the flames were fought by 80 fire fighters from across Dorset using 16 fire appliances.

All day today they are monitoring the two hectares of scorched heath, quickly damping down hot spots as they arose.

“It was deliberate,” he said.

“There were four different seats of fire, which is unusual. That leads us to say it was deliberate. The police are investigating that, from their side.”

He described the fire as “large” and it was apparent that there had been seats of fire both sides of a popular track along the protected heath, widely used by dog walkers and cyclists.

He said crews had been helped by the fact that it was at cooler at night, and he said there had been a four knot wind from the north-west. Multi-agency specialist teams were quickly on site and they used off road vehicles to get to the blaze.

Dorset Fire and Rescue was called at around 10.30pm to the site near Mannings Heath.

It said firefighters were dealing with “multiple seats of fire” close to the Tower Park roundabout.

At 11.49pm, the service said the fire had been surrounded and was being brought under control.

By midnight, the flames were out and the service was damping down.

Chief Inspector Caroline Norton said that Dorset Police had launched an investigation and that anyone with information was asked to call 101.

The fire brought hundreds of  people out of their homes to watch. It closed some of the surrounding roads for part of the evening.

Dorset Fire and Rescue said it had received 65 calls about the blaze.

Jez Martin, nature conservation officer for the Borough of Poole, said it was difficult to fully assess the damage in the dark.

Photo: Jack Oxenbury

But he said the fire looked to have spread to around a hectare of heathland.

“The fire service has done a good job in putting this fire out but it has damaged an important part of the heath which could take 15-20 years to recover,” said Mr Martin.

“There were four to six separate seats of fire so this was quite a deliberate action to set fire to a fragile area of heathland,” he said.

He said most heath fires started from only one seat of fire.

“We have had this before happen on Canford Heath but not for many years. Its a concern that someone has put in a lot of effort to get a fire going,” he added.

As well as destroying a Dartford warbler's nesting site, the arsonists would have destroyed hundreds of reptiles, including common lizards and slow worms but possibly rarer species as well, he added.

The fire service's incident commander, Andy Fox, said it was “unusual” to face a fire started in six separate places.

He said the service had directed a lot of equipment at the fire early on to stop it spreading.

“It's a really good multi-agency fire response,” he said.

“We've had the police helicopter up giving us reports of the fire's direction and helping direct fire fighters on the ground.”

As of 12.30am, he expected to have fire fighters on the scene for another couple of hours damping down.

The service would visit the site again later on Wednesday morning for a reassessment, he said.

The fire service Tweeted at around 1.20am that relief crews were being sent to take over from the original firefighters.

It said at 2am that a Red Cross welfare vehicle was supplying fire fighters with drinks.

Incident at Canford Heath now scaled down to the relief crews of 2 off road fire engines and 2 landrovers who are currently damping down

— Dorset Fire Control (@DFRSFireControl) July 17, 2013