Malaysia Airlines Flight MH370 - missing since March 8 - is now presumed to have crashed in the Indian Ocean killing all 239 people on board, stunned relatives were told last night.
The announcement was made after new information came to light about the plane's last known location.
Malaysian Prime Minister Najib Razak said investigators at the UK's Air Accident Investigation Branch had concluded the plane flew along the so-called southern corridor.
They said its last position was in the middle of the Indian Ocean thousands of kilometres west of Perth, Australia.
Razak said in a televised press conference: "This is a remote location, far from any possible landing sites.
"It is therefore with deep sadness and regret that I must inform you that according to this new data, flight MH370 ended in the southern Indian Ocean."
The news devastated relatives of the 154 Chinese passengers, who were suddenly called to meetings in Beijing's Lido Hotel and at a hotel in Kuala Lumpur to hear the announcement.
Screams, tears and cries of disbelief immediately filled the Lido Hotel meeting.
"I can't take this," shouted a middle-aged woman as she staggered out of the room, supported by two men. A man screamed: "Why is the Malaysian government doing this to us?"
Paramedics were called and one middle-aged woman was carried out of the room on a stretcher. Other relatives refused to believe the news.
"Malaysia is lying. Make China go down there and look," one relative told the South China Morning Post by text message.
Another said: "If they don't show us the actual plane itself then it doesn't mean anything."
Relatives in Kuala Lumpur were expected to board a plane to Perth today.
Watch: MH370 relatives in China distraught as hope extinguished
Malaysia Airlines also released a statement last night. It said: "We deeply regret that we have to assume beyond any reasonable doubt that MH370 has been lost and that none of those on board have survived. "We must now accept that all evidence suggests the plane went down in the Southern Indian Ocean."
China's foreign ministry demanded the Malaysian authorities provide all the information and evidence they have about the plane.
In a meeting late Monday, Deputy Foreign Minister Xie Hangsheng asked Malaysia’s Ambassador to China, Iskandar Bin Sarudin, to provide the “detailed evidence” that led to the conclusion, China’s Ministry of Foreign Affairs said.
“We demand the Malaysian side to state the detailed evidence that leads them to this judgement as well as supply all the relevant information and evidence about the satellite data analysis,” Xie said, according to a statement on the ministry’s website.
“The search and rescue work cannot stop now, we demand the Malaysian side to continue to finish all the work including search and rescue,” Xie said.
Soon after the solemn news was announced, Malaysia Airlines told relatives of those on board a jet that crashed in the Indian Ocean that they would be brought to the “recovery area”, as the search for wreckage goes on.
“When Malaysia Airlines receives approval from the investigating authorities, arrangements will be made to bring the families to the recovery area.”
It did not specify where the relatives would be taken, but the international search effort - focused on a remote stretch of the southern Indian Ocean - has seen aircraft and ships depart from Perth, on Australia’s west coast.
The extraordinary turn of events came at the end of a day when two separate search teams said they had spotted "objects" floating in the Indian Ocean.
A Chinese team was reported to have seen two large white floating objects, while Australian officials said an aircraft crew had seen two items, one grey or green and circular, and the other orange and rectangular.
Ships rushed to the location to hunt for the suspected debris. Malaysian officials said it was understood some items would be recovered by this morning.
Malaysian authorities have been widely criticised for their handling of the 18-day hunt for MH370, with accusations of incompetence and cover-ups.