A Malaysia Airlines jet carrying 295 people has crashed in east Ukraine on a flight from Amsterdam to Kuala Lumpur.
There are no signs of survivors at the scene of the crash near the village of Grabovo, in rebel-held territory close to the border with Russia.
Both sides in Ukraine's civil conflict accused each other of shooting down the plane with a missile. It is still not clear why the plane came down.
It is the second disaster suffered by Malaysia Airlines this year.
Flight MH370 disappeared en route from Malaysia to China in March and still has not been found.
At a news conference at Schiphol airport, Malaysia Airlines' European chief Huib Gorter said they were still trying to identify some of the passengers from flight MH17.
He said of the passengers that have been identified there were:
- 154 Dutch nationals, 27 Australians, 23 Malaysians, 11 Indonesians
- Six Britons, four Germans, four Belgians, three from the Philippines and one Canadian
- All 15 of the crew were Malaysian
Other airlines have announced they are now avoiding eastern Ukraine.
Analysis: Jonathan Marcus, BBC News
If it does turn out that the Boeing 777 was shot down by the separatists - with weaponry supplied by Moscow - then it could significantly alter the terms of the whole debate surrounding the Ukraine crisis.
Over the past few days there has been growing concern among Western governments that Russia was stepping up its military support for the separatists in eastern Ukraine.
Nato spokesmen insist that more and more heavy military equipment has moved from Russian stockpiles to the separatists across the border.
In response, the United States has strengthened its economic sanctions against Moscow - it is threatening even stronger action - though the European Union has so far failed to follow Washington's lead.
But if Russia in any way had a hand in this tragedy then the pressure - especially on the Europeans - for much tougher sanctions will only grow.
Malaysian Prime Minister Najib Razak spoke of his shock and said he was launching an immediate inquiry into the crash.
"This is a tragic day in what has already been a tragic year for Malaysia," he said.
US and Ukrainian officials said they believed the plane had been brought down by a missile.
Ukrainian President Petro Poroshenko said it was an "act of terrorism".
Foreign Minister Pavlo Klimkin told the BBC he had intercepted phone conversations that proved the plane was shot down by pro-Russian separatists.
But Russian President Vladimir Putin blamed the Ukraine government for restarting military operations in the area, where it is trying to regain control from pro-Russian rebels.
"The country in whose airspace this happened bears responsibility for it," he said.
Separatist leader Alexander Borodai accused the Ukrainian government of downing the airliner.
Ukraine's defence ministry issued a statement saying there were no air force jets in the area and no surface-to-air systems being used against the rebels.
The British government has called for an emergency meeting of the UN Security Council to discuss the crisis in Ukraine as a result of the crash.
The plane fell between Krasni Luch in Luhansk region and Shakhtarsk in the neighbouring region of Donetsk.
At least 100 bodies have been found so far at the scene, an emergency services worker told Reuters news agency, with wreckage spread across an area of up to about 15km (nine miles) in diameter.
Broken pieces of the wings were marked with the blue and red paint of Malaysian Airlines.
"I was working in the field on my tractor when I heard the sound of a plane and then a bang and shots," a witness called Vladimir told Reuters.
"Then I saw the plane hit the ground and break in two. There was thick black smoke."
A separatist rebel from nearby Krasnyi Luch who gave his name as Sergei said: "From my balcony I saw a plane begin to descend from a great height and then heard two explosions."
The head of the Russian Air Traffic Controllers' Union, Sergei Kovalyov, told BBC Russian that the airspace over eastern Ukraine had remained open during the conflict because the planes previously shot down had tended to be helicopters or low-flying fast jets.
"In order to bring down an airplane from an altitude of 10,000m, you need to have very serious weapons…. missiles," he said. "It's either a mistake or a terrorist act."
Ukraine has accused Russia's military of supplying advanced missiles to the rebels.
Earlier on Thursday, Ukrainian officials blamed the Russian air force for shooting down one of its ground attack jets on Wednesday, and a transport plane on Monday.
In 2001, Ukraine admitted its military was probably responsible for shooting down a Russian airliner that crashed into the Black Sea, killing all 78 people on board.
Malaysia Airlines Flight MH17 - Amsterdam to Kuala Lumpur
Aircraft: Boeing 777-200ER
Left Amsterdam: 10:15 GMT
Lost contact: 14:15 GMT at 10,000m (33,000ft)