At least 27 Australians are among 298 passengers who were killed after their Malaysia Airlines flight crashed in east Ukraine.
Foreign Minister Julie Bishop has confirmed at least 27 Australians were among the dead but said that number could be higher as more details emerge.
"I can confirm 27 passengers on that flight were Australian nationals," she said.
"This is a terrible tragedy. We don't know the cause but there is speculation that the plane was shot down.
"If that is the case it is an unspeakable crime."
Malaysia Airlines announced on social media the loss of the Boeing 777 carrying 280 passengers and 15 crew, which had been expected in the Malaysian capital at around 6am (8am AEST) on Friday.
Ms Bishop said Australian officials were seeking permission to access the crash site, which was in rebel held territory in eastern Ukraine.
She said Australia would demand a full, independent international inquiry into the crash, amid reports Russian separatists have taken the plane's black box.
"Regardless of the circumstances we urge the separatists to co-operate with an investigation into this crash," Ms Bishop said.
'Blown out of the sky'
Malaysia Airlines flight MH17 was enroute to Kuala Lumpur from Amsterdam when it was reportedly hit by a missile.
US Vice-President, Joe Biden, has said the plane was 'blown out of the sky.'
"(It 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."
Ukraine's government and pro-Russian insurgents traded blame for the disaster, with comments attributed to a rebel commander suggesting his men may have downed Malaysia Airlines flight MH17 by mistake, believing it was a Ukrainian army transport plane.
The official spokesman for President Petro Poroshenko said he believed pro-Russian insurgents downed the jet and said the "incident is not a catastrophe. It is a terrorist act".
The Ukrainian leader said earlier that "the Ukraine Armed Forces did not fire at any targets in the sky" and vowed "those behind this tragedy will be brought to justice".
Ukraine rebels have since said they are ready for temporary truce following plane crash.
'It was like an earthquake'
Shocked local residents struggled to take in the scene of the carnage and said that remnants of the jet had been found in a village some 9 kilometres from the centre of the crash site.
Some locals said the impact felt "like an earthquake" in their village of Grabove, near the Russian border.
"I had just gone to sleep at around 1600 (1300 GMT) when I heard an enormous bang," Katya, 64, told AFP. "It was like an earthquake."
Her daughter Natalya, 36, said that she had fled to safety when the sound of the explosion rumbled overhead.
"I took my baby and went and hid in the basement," she said.
There was no sign of survivors at the crash site near the rebel-held town of Shaktarsk in the Donetsk region, where journalists have reported seeing dozens of severely mutilated corpses strewn through the smouldering wreck of the decimated airliner.
International shock
Malaysia's Prime Minister Najib Razak said on Twitter he was "shocked by reports that an MH plane crashed" and announced an "immediate investigation".
Boeing said it was ready to assist the authorities in any way following the crash.
"All our thoughts and prayers go to the people on board the Malaysia Airlines plane missing in Ukrainian airspace, as well as their families and friends," it said in a statement.
The Kremlin said President Vladimir Putin and US President Barack Obama - at loggerheads over a new wave of US sanctions over Ukraine - had discussed the crash.
Obama called it a "terrible tragedy" and said US officials were trying to establish if any Americans were on board.
Australian politicians have also offered their condolences with Senators holding a minute's silence in the Senate.
Greens leader Christine Milne also addressed the Senate, telling colleagues that a number of victims were en-route to an AIDS conference in Melbourne.
Some politicians have taken to social media to share their condolences, paying tribute to the 298 people who were killed on the Malaysia Airlines jet MH17 when it crashed over Ukraine.
