Australian officials say the search for the missing Malaysia Airlines plane has been suspended because of bad weather.
The Australian Maritime Safety Authority (Amsa) said high winds and rain meant planes could not fly safely.
Malaysian PM Najib Razak says satellite data showed the plane ended its journey in remote seas west of Australia.
Relatives of those on board have voiced grief and anger, while China has demanded to see the satellite data on which that conclusion was based.
Malaysia Airlines flight MH370 disappeared on 8 March as it flew from Kuala Lumpur to Beijing. It was carrying a total of 239 people, including 153 Chinese nationals.
A multinational search effort has focussed on seas some 2,500km (1,500 miles) to the southwest of the Australian city of Perth.
But in a news conference late on Monday, the Malaysian leader said it had to be concluded "with deep sadness and regret" that according to new data "flight MH370 ended in the southern Indian Ocean".
In Malaysia, newspapers ran black or darkened front pages in tribute to those now believed to have died.
In Beijing, relatives of passengers on board the plane released a statement accusing the Malaysian government of trying to "delay, distort and hide the truth".
Dozens of them then left their Beijing hotel on a protest bound for the Malaysian embassy, carrying banners asking Kuala Lumpur to be truthful with the relatives.
Planes from several nations have been scouring waters far off Perth for signs of the missing plane, in a search co-ordinated by Australia.
There have been several sightings of debris, but none have yet been confirmed as linked to the plane.
In its statement, Amsa said it had undertaken a risk assessment "and determined that the current weather conditions would make any air and sea search activities hazardous and pose a risk to crew".
"Therefore, Amsa has suspended all sea and air search operations for today due to these weather conditions," it said.
Search operations should resume on Wednesday if weather conditions permit, Amsa added.
China, meanwhile, has asked Malaysia to hand over the data that led it to conclude the plane had flown into the sea.
"We demand the Malaysian side 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," Chinese Deputy Foreign Minister Xie Hangsheng said, according to a statement on the ministry's website.
"The search and rescue work cannot stop now. We demand the Malaysian side continue to finish all the work including search and rescue," he added.
Mr Najib, in a sombre late-night news conference in Kuala Lumpur, said the conclusion the plane was lost was based on new satellite analysis by British firm Inmarsat, and information from the UK's Air Accidents Investigation Branch (AAIB).
The firms had "concluded that MH370 flew along the southern corridor, and that its last position was in the middle of the Indian Ocean", Mr Najib said.
"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."
