A Boeing 787 Dreamliner operated by Ethiopian Airlines caught fire at Britain's Heathrow airport on Friday in a fresh blow for the US planemaker whose new model was grounded for three months after one high-tech battery caught fire and another overheated.

External scorching from the fire was located in a different part of the aircraft from the bays containing batteries, and the cause of the fire was unknown.

Boeing shares closed down 4.7 per cent at $101.87, knocking $3.8 billion off the company's market capitalisation after television footage showed the Dreamliner surrounded by firefighting foam at Heathrow.

Heathrow briefly closed both its runways to deal with the fire which broke out while the aircraft was parked at a remote stand. There were no passengers aboard the plane.

Pictures of the plane at Heathrow showed an area just in front of the tail that appeared to be scorched.

The Dreamliner's two batteries are in electrical compartments located low down and near the front and middle of the plane, while the visible damage to the Ethiopian plane appears to be on top of the fuselage, further toward the rear, according to video from the scene.

"A Boeing 787 Dreamliner suffered an on board internal fire," a Heathrow spokeswoman said. "The plane is now parked at a remote parking stand several hundred metres away from any passenger terminals."

Former US National Transportation Safety Board chairman Mark Rosenker said the Heathrow incident was extraordinary news, coming so soon after the fleet had returned to service, but he cautioned against jumping to conclusions.

"It's very early. No one knows where the fire started at this point," Rosenker told Reuters, adding it could be something as simple as a coffee pot left on in a galley.

Boeing said it was aware of the fire and it had people on the ground working to understand the causes of it. The US Federal Aviation Administration said it was in contact with Boeing.

A spokesman for GS Yuasa, which makes the Dreamliner batteries, said he had not received any information on the London fire.

The 787 is Boeing's biggest bet on new technology in nearly 20 years. It cost an estimated $32 billion to develop and Boeing plans to use hundreds of innovations such as its carbon-fibre composite skin and electrical system to enhance other jets.

Boeing never disclosed the cost of the three-month grounding, which ended in April, but said it absorbed most of the expense in the first quarter while still posting a 20 per cent rise in profit, and its shares are up 35 per cent this year, even after Friday's loss.

The plane which caught fire in London was the first of the 787 fleet to resume flight after the battery-related grounding.

"This is terrible for the Dreamliner, any event involving fire and that airplane is going to be a PR disaster for Boeing," Christine Negroni, an aviation writer and safety specialist based in New York, said in a telephone interview.

"Because of the battery issue, the public is even more sensitive to events that happen to the Dreamliner. Even if they are normal, benign teething problems, that subtlety is going to be lost on the public," she said.

Another Boeing Dreamliner operated by Thomson Airways returned to Britain due to technical issues on Friday as a precaution, TUI Travel said.

Ethiopian Airlines said its aircraft had been parked at Heathrow for more than eight hours before smoke was detected.

Richard Aboulafia, a senior aerospace analyst at the Teal Group in Virginia, said early evidence, including images of the jet, suggest the battery is not the issue because of the location of the fire.

Another person familiar with the aircraft's configuration said the damaged area appears close to galleys and environmental control systems, but added that it was too early to link the fire to any specific equipment.

Boeing's 787 Dreamliner was grounded by regulators in January after batteries overheated on two of the jets within two weeks, including a fire in a parked Japan Airlines plane in Boston.

Boeing was forced to halt deliveries of the jet while it was grounded and airlines stopped ordering the plane during that period. Orders have since resumed and Boeing has logged 83 Dreamliner orders this year, bringing its current order book to 930 planes.

The Dreamliner resumed flying in April, with Ethiopian Airlines being the first carrier to put it back into passenger service.-Reuters