Relatives of the 239 people on the doomed Malaysia Airlines plane screamed in anguish as they were told the jet had crashed - by text message.
Sky's Jonathan Samuels, in Beijing, said there were "very, very distressing" scenes as Malaysia Airlines broke the news.
"Some people were in tears, others are helping those struggling and a woman is screaming in absolute anguish. It's very tough to watch," he said.
The text message said: "Malaysia Airlines deeply regrets that we have to assume beyond any reasonable doubt that MH370 has been lost and that none of those on board survived.
"As you will hear in the next hour from Malaysia's Prime Minister, we must now accept all evidence suggests the plane went down in the Southern Indian Ocean. "
Malaysia Airlines stressed they did not only inform relatives by text message but informed them "via all channels".
TV pictures showed distressed families being helped away amid chaotic scenes in the Lido Hotel in Beijing.
Paramedics treated some people who were overcome by grief.
Relatives were told of the jet's fate around 30 minutes before Malaysian Prime Minister Najib Razak told a news conference the plane had crashed.
UK satellite data confirmed flight MH370 crashed into the southern Indian Ocean.
The flight vanished from civilian radar screens less than an hour after take-off from Kuala Lumpur on March 8.
No confirmed sighting of the plane has been made, but debris found in remote waters off Australia might be from the missing plane.
Families of the passengers will be taken on chartered flights to Australia, according to Sky News sources.