SYDNEY, Australia — Government officials and families of passengers lost on a Malaysian jet that vanished last year with 239 people aboard responded warily on Thursday to the discovery of possible wreckage from the aircraft, reluctant to fan hopes after more than a year of fruitless searching and false rumors.
Deputy Prime Minister Warren Truss of Australia, whose country has led the search for the jet, Malaysia Airlines Flight 370, said that the discovery of an airplane part thousands of miles from the search area was “a very significant development” but cautioned against concluding that it was from the missing aircraft.
“It is too early to make that judgment,” Mr. Truss said at a news conference in Sydney. “But clearly we are treating this as a major lead and seeking to get assurance about what has been found and whether it is indeed linked to the disappearance of MH 370.”
American investigators have concluded, based on photographs and videos, that the object discovered on Wednesday on Réunion, a remote French island off the coast of Madagascar, is from a Boeing 777, making it likely that it came from Flight 370. No other Boeing 777 is known to be missing, investigators said.
Prime Minister Najib Razak of Malaysia said the debris would be sent to Toulouse, France, the site of the nearest office of the French aviation safety bureau, known as BEA. “A Malaysian team is on the way to Toulouse now,” Mr. Najib said in a statement, adding that a second team was en route to Réunion.
“We have had many false alarms before, but for the sake of the families who have lost loved ones, and suffered such heartbreaking uncertainty, I pray that we will find out the truth so that they may have closure and peace,” Mr. Najib said in the statement. “I promise the families of those lost that whatever happens, we will not give up.”
The object, which a French official said appeared to be a wing flap about nine feet long and three feet wide, was discovered by workers cleaning a beach on the island, which is thousands of miles from the area off Western Australia where the search for debris from Flight 370 has been underway.
That search area was determined by analyses of satellite images and signals automatically transmitted from the plane. Australian officials said that the search in that area would continue, and that it was possible for ocean currents and winds to have carried debris to Réunion from there.
The French Justice Ministry and the Réunion authorities said in a joint statement on Thursday that “at this stage, the origin of the debris is not identified.”
“No hypothesis can be ruled out, including that it originates from a Boeing 777,” the statement said.
Mr. Truss said that a number found on the part, BB670, was not a serial number or a registration number but could be linked to the maintenance of the aircraft, which would help identify it. He said scientists had been asked to examine photographs of barnacles that were on the object to try to establish how long it had been submerged.
Flight 370 vanished on March 8, 2014, en route to Beijing from Kuala Lumpur, the Malaysian capital. It inexplicably went off course midflight and flew south for hours before running out of fuel and crashing into the southern Indian Ocean, according to investigators. The pilot stopped communicating with air traffic controllers about 40 minutes into the flight.
Jason Middleton, the head of the aviation school at the University of New South Wales in Australia, said that if the debris was confirmed to be from Flight 370, it could provide some clues to what happened to the plane, but not to the whereabouts of the rest of the wreckage.
“Depending on the nature of the damage to that part, they will be able to tell how it separated from the rest of the plane,” Mr. Middleton said. “The twisted structure and the technical aspect of how it separated will give a reasonable indication of how violent the impact was.”
Joe Hattley, a spokesman for Australia’s transportation safety bureau, cautioned against raising hopes for family members of those aboard the jet.
“We have had lots of debris reported to us,” Mr. Hattley said. “This one is more promising. Any piece of information is good information, but I am mindful of the next of kin and how difficult this could be for them.”
Jiang Hui, a telecommunications engineer in Beijing whose mother was on Flight 370, said that relatives were treating the development with caution. “We’ve often had these reports that are overstated or incorrect, saying they’ve found something,” he said.
“After more than a year of this our hearts are broken, and after last night’s news, a lot of family members were really agitated,” Mr. Jiang added.
Most of the passengers on Flight 370 were Chinese. Hong Lei, a spokesman for the Chinese Ministry of Foreign Affairs, said that the government in Beijing was paying close attention to the news, but he offered no other details about the possible wreckage from Flight 370.
“We have taken note of the report, and further verification is being conducted with relevant countries,” Mr. Hong said in a statement issued on the ministry’s website. “The Chinese side will follow closely how this plays out and properly handle relevant follow-up matters.”
Paul Kennedy, the search director for Fugro Survey, a division of a Dutch company hired by Australia to conduct the seabed search for Flight 370 off Western Australia, said the work there was continuing as usual.
“There’s no substantial change to where we are looking,” said Mr. Kennedy, who for months has pored over images from the ocean floor. “We’ve just got to all be patient right now. And fingers crossed.”