A new theory has emerged that the missing Malaysia Airlines plane may have flown on for hours beyond its last reported sighting – adding a new twist to a saga of conflicting details and misinformation in the still fruitless search for flight MH370.



As Malaysia and Vietnam sent aircraft on Thursday to an area of the South China Sea where China said satellite photos showed possible wreckage, the Wall Street Journal reported that the plane had still been automatically sending data back to Boeing well after the time that authorities have said it dropped off radar screens.



The last definitive sighting of the aircraft on civilian radar came shortly before 1.30am on Saturday, less than an hour after taking off from Kuala Lumpur, as it flew north-east across the mouth of the Gulf of Thailand bound for Beijing. The Wall Street Journal, citing two people in the US familiar with the details, said US investigators suspected the Boeing 777 actually stayed in the air for about four hours past that time.



The startling assessment was based on data automatically sent by the plane to Boeing’s engine department as part of a routine maintenance and monitoring program, the Journal said.



The report adds to a pile of speculation and confused accounts of the plane’s last movements. It raises the possibility that the plane, and the 239 people on board, could have flown on for hundreds of additional miles under conditions that remain murky. Authorities remain uncertain about which ocean to search for the jetliner, which went missing on Saturday after taking off from Kuala Lumpur.



On Thursday planes continued searching for three possible floating objects that appeared in Chinese satellite images not far from the plane’s original flightpath. Beijing urged caution, emphasising that it might amount to nothing. Vietnamese military officials said on Thursday that they had already searched the area earlier and turned up nothing but had sent an aircraft back anyway.



“It is true that the satellite was launched and detected some smoke and what were suspected metal shreds about 37km (23 miles) south-west of Ho Chi Minh City,” said China’s civil aviation chief, Li Jiaxing. “But after some review we cannot confirm that they belong to the missing plane.”



It was unclear why Chinese authorities had not alerted Malaysia to the debris earlier. Malaysia’s civil aviation chief told the Associated Press early on Thursday that he had only learned of the floating objects from news reports. An army official in Vietnam said authorities there were only alerted to the objects on Thursday and were verifying the information, Malaysia’s Star newspaper reported.



Malaysia’s transport minister, Hishammuddin Hussein, confirmed on Thursday that Malaysian authorities were looking into the lead. “Bombardier has already been dispatched to investigate alleged claims of debris found by Chinese satellite imagery,” he said on Twitter, apparently referring to a Canadian-made Bombardier aircraft being sent on the mission.



Malaysia’s civil aviation chief Adbul Rahman cautioned: “There have been lots of [previous] reports of suspected debris.”



Authorities have become increasingly desperate for a breakthrough, with teams plying 35,800 square miles, a vast expanse the size of Portugal ranging from the waters off Vietnam in the South China Sea to the Malacca Strait, parts of peninsular Malaysia and out towards the Andaman Sea.



The Chinese satellite information draws the 12 nations currently searching for the missing plane back towards where the search and rescue originally began, putting MH370 near where authorities initially said the last radar connection with the flight was at 1.30am. There have been other official statements that it showed up again at 2.30am near Malaysia, and just before that at 2:15am near the Malacca Strait.



Malaysian authorities said the search effort would stay focused on the South China Sea and the strait of water towards the Andaman Sea.



Flight MH370 vanished from civilian radar screens at 1.30am on Saturday between Malaysia and southern Vietnam in the Gulf of Thailand. It sent no distress signal and the pilots’ last transmitted message was “All right, good night”, a pleasantry to Malaysian air traffic controllers that gave no indication anything was wrong.



Sightings of potential wreckage have turned out to unrelated to the missing jet, and have included oil slicks and possible life rafts – one of which turned out to be a moss-covered cable reel and another that authorities said probably came from a sea vessel.



The growing frustration at being unable to locate the plane has frayed relations between Malaysia and China as nearly two-thirds of the passengers on MH370 were Chinese citizens.



The Chinese premier, Li Keqiang, made a barbed remarked at Malaysian authorities on Thursday, telling reporters during his annual press conference: “The Chinese government has asked the relevant party to enhance co-ordination, investigate the cause, locate the missing plane as quickly as possible and properly handle all related matters.”



The disappearance has led to massive speculation over what might have caused the plane to vanish from radar screens. Authorities have considered hijacking, sabotage, psychological or personal problems among crew or passengers.



Confusion even reigned over whether the particular 777 involved was subject to a safety alert from the US Federal Aviation Administration about cracks possibly developing in the fuselage around a satellite antenna. The FAA said the alert had been sent to 777 operators and was relevant to MH370 but Boeing told Reuters the Malaysia Airlines plane did not have the antenna and was unaffected.



Hussein, the Malaysian defence minister, told a press conference on Wednesday that “we have nothing to hide” amid claims Malaysia was not divulging all the facts. “There is only confusion if you want to see confusion,” he said.



The US said its satellite images had been checked for any sign of a mid-air explosion but nothing was found.