Firefighters have finally entered a power station that erupted in flames early today.

The fire is now said to be under control, with crews working in arduous conditions inside the Tilbury Power Station building.

But the incident, which at its height involved 120 firefighters, is likely to be a protracted one.

Thick black smoke could be seen earlier today from Gravesend down to Higham and beyond after the fire started at Tilbury Power Station, on the opposite side of the River Thames.

Speaking about the crews fighting the intense blaze, chief fire officer David Johnson said: "They are doing an absolutely fantastic job in dangerous and punishing conditions. Inside the building it's hot, full of smoke and extremely dusty.

"We expect the fire to be out within the next two to three hours if everything goes according to plan."

Flames were coming from high up in the main building - a wood pellet hopper containing 2,100 tonnes of machinery - and warning sirens could be heard.

The fire broke out in a fuel storage area about 7.45am and around 100 firefighters were quickly on the scene, according to Essex Police.

The whole building was heavily smoke-logged and firefighters were trying to assess how to tackle the blaze.

Chief fire officer Johnson, in charge of the incident, said initially: "The safety of our crews is paramount. Because of the position of the fire and the structure of the building it is not safe to commit them to the building immediately. We are getting as close as we can.

"The fire involves some 4,000 tonnes of fuel in storage cells."

Several high voltage power cables were isolated by the fire service who using three aerial ladder platforms among their 17 engines at the scene.

Less than an hour after the fire broke out, a second fire started in a pile of wood close to berths 27 and 28 at Tilbury Docks. That was soon dealt with.

However, the incident at the power station was still not under control at 11.30am.

Chief fire officer David Johnson said this was one of the most challenging fires he had had to deal with in his 20-year career because of the technical complexities.

The number of firefighters involved had risen to 120 by late morning. They are using helicopters to survey the building and identify hot spots, while inside the building a decision has been taken to fight the fire with foam.

The power station has been closed down.

Mr Johnson said the fire now involved up to 6,000 tonnes of material high in the roof of the power station.

It is the material used to drive the power station. It is imported from Europe by ship.

The same material caught fire aboard a ship a few weeks ago, sparking another major emergency for the Essex fire service.

Mr Johnson admitted the fire is not yet under control.

He added: "We expect this to be a protracted incident going on for some hours, if not days."