Global demands mounted Friday to find those responsible for apparently shooting down a Malaysian airliner over rebel-held eastern Ukraine as relatives around the world mourned the deaths of the 298 people on board.

Local emergency crew picked through terrible carnage at the crash site of Malaysia Airlines (MAS) Flight MH17, placing dozens of sticks with white rags in the ground to mark where bodies lay.

The Boeing-777 came down in cornfields in the separatist-held region on Thursday, spraying debris and body parts for kilometres around, with the United States claiming it was shot down in a missile attack.

Kiev accused pro-Russian separatists battling Ukrainian forces of committing a "terrorist act" as stunned world leaders urged a full investigation into the disaster, which could further fan the flames of the worst East-West crisis since the Cold War.

The United States demanded an "unimpeded" international inquiry into the tragedy and rejected Russian President Vladimir Putin's charge that Ukraine's crackdown on separatist rebels stoked tensions that led to the crash.

"While we do not yet have all the facts, we do know that this incident occurred in the context of a crisis in Ukraine that is fuelled by Russian support for the separatists, including through arms, material, and training," the White House said in a statement.

News of the crash sent world stock markets tumbling. Shares in Malaysia Airlines, still afflicted by the trauma and global stigma of flight MH370's disappearance four months ago, plummeted almost 18 percent on Friday morning.

The father of one MH17 stewardess wept as he expressed the vain hope his daughter could be alive.

"We are just hoping she survived even though we know many are dead... We pray that somehow she is safe and comes home," Salleh Samsudin, 54, said of 31-year-old Nur Shazana Salleh on Malaysian television.

One devastated relative told how her sister Ninik Yuriani, 56 – of Indonesian descent but a Dutch national – was on her way to Jakarta to celebrate the Muslim festival Eid.

"My family is now gathered at my sister's house in Jakarta. We've decided to keep this from my mother. She's so old and weak, I don't think she could take it," Enny Nuraheni, 54, told AFP.

In the Netherlands, tears welled up in the eyes of Sander Essers, who lost several relatives in the crash, as he told AFP he had spoken to his brother just 20 minutes before he boarded.

"I can't tell you what he told me."

International fury

Scores of mutilated corpses and body parts were strewn around the smouldering wreckage in the village of Grabove, near the Russian border. Shocked residents of the village said the crash impact felt "like an earthquake".

MAS said 283 passengers and 15 crew were aboard the plane – including at least 173 Dutch nationals, 43 Malaysians, 28 Australians and 12 Indonesians.

As many as 100 of those killed were delegates heading to Australia for a global AIDS conference, the Sydney Morning Herald reported.

Australian Prime Minister Tony Abbott said the crash was "not an accident, but a crime" and blasted Russia's response to the downing of the jet as "deeply unsatisfactory".

Local rescue workers at the scene told AFP that at least one of the plane's black boxes had been found and mediators said rebels had committed to allowing international investigators "safe access" to the site, as President Barack Obama has warned against tampering with evidence among scattered debris.

Interpol offered its "full assistance" to help identify and repatriate corpses.

The UN Security Council called an emergency session on Friday to discuss the disaster and British Prime Minister David Cameron called a crisis meeting of top officials.

Comments attributed to a pro-Russian rebel chief suggested his men may have downed the plane by mistake, believing it to be a Ukrainian army transport aircraft.

Ukraine released recordings of what they said was an intercepted call between an insurgent commander and a Russian intelligence officer as they realised they had shot down a passenger liner.

However the rebels accused the Ukrainian military of shooting down the plane and Russia's defence ministry said Friday it had data indicating that a Ukrainian missile system was operating in the area.

Putin has said Ukraine bears responsibility for the crash and said it underscored the need for a "peaceful settlement" to the Ukraine crisis in talks with Dutch Prime Minister Mark Rutte.

The disaster comes just months after MAS' Flight MH370 disappeared on March 8 with 239 on board. That plane diverted from its Kuala Lumpur to Beijing flight path and its fate remains a mystery despite a massive multinational aerial and underwater search.

"This is a tragic day, in what has already been a tragic year, for Malaysia," Malaysia's Prime Minister Najib Razak told reporters early Friday after announcing an "immediate investigation".

Najib added that a team of disaster response specialists had been dispatched to Kiev and that authorities in Ukraine had agreed to try to establish "a humanitarian corridor to the crash site".

'Blown out of the sky'

German Chancellor Angela Merkel urged an immediate ceasefire to allow what Obama demanded should be a "prompt, full, credible and unimpeded international investigation."

But fighting that had claimed over 600 lives prior to the plane crash continued and an AFP crew at the site reported hearing sporadic heavy weapons fire.

Top separatist leader Alexander Borodai agreed to allow investigators access to the crash site but said there was "no question of a ceasefire."

Two US officials told AFP that intelligence analysts were reviewing the data to see whether the missile used to down the aircraft was launched by pro-Moscow separatists, Russian troops across the border or Ukrainian government forces.

"We are working through all the analysis," said one official, adding that there was little doubt that the plane was struck by a surface-to-air missile.

In Detroit, US Vice President Joe Biden said the plane was "apparently... and I say apparently because we don't have all the details yet... shot down. Not an accident. Blown out of the sky."

Ukrainian Prime Minister Arseniy Yatsenyuk alleged Friday that the rebel's Russian backers had gone "too far" and called for those behind the tragedy to be tried in The Hague.