Image caption The plane was carrying 42 people

Boeing has halted test flights of its long-delayed 787 Dreamliner after a fire forced an emergency landing in Texas on Tuesday.

Boeing said it was the most serious incident since it began test flights of the jet last year.

The planemaker's shares fell 3.2% in New York as investors worried about the risk of a further delay to the aircraft's launch.

The Dreamliner is already nearly three years behind schedule.

"We have decided to not fly the other planes until we better understand the incident," a spokeswoman said.

"I don't know how long the suspension will last."

Boeing said it would take time to determine what caused the fire, which saw smoke enter the plane during the approach to Laredo, Texas on a routine test flight from Yuma, Arizona.

All 42 people on board were evacuated safely using emergency chutes in what was the first high-profile incident for the 787 under testing.

Boeing said it had no reason to suspect that the aircraft's engines, which are made by Rolls-Royce, had anything to do with the incident.

Rolls is under pressure to allay concern about the failure of a Trent 900 engine on a Qantas Airbus A380 last week.

Boeing's 787s are equipped with Rolls-Royce Trent 1000 engines.

Being built in Seattle, the Dreamliner is Boeing's most sophisticated plane yet. The company claims it is lighter, faster and emits less CO2 than similar-sized planes currently flying.

It made its maiden flight in December 2009.