Australian Prime Minister Tony Abbott fears the remains of some Australian victims of the MH17 crash haven't been collected.
A number of body and body parts are due to be transported by air from the Ukrainian city of Kharkiv to the Netherlands on Wednesday night (local time).
But Abbott said based on an inspection of the train carriages travelling from the crash zone, many of the bodies of the almost 300 victims - including Australians - were uncollected.
''It is quite possible that many bodies are still out there in the open in the European summer subject to interference and subject to the ravages of heat and animals,'' he told reporters in Canberra.
The prime minister has ''serious concerns'' about the collection of the remains.
''It has been up until now quite unprofessional,'' he said.
''As long as it's possible that there are any Australian remains out there we owe it to the families to do our utmost to recover them.''
Abbott said a proper forensic search could only happen if the area was properly secured.
The government is considering options to create a safe environment for the forensic search, which could involve a cordon to bar anyone except investigators from the crash site.
More work with Australia's ''partners in grief'' at the United Nations could be done to strengthen the UN Security Council resolution.
''(That would) make it reality that we do, in fact, bring them all home,'' Abbott said.
Interference at the site of downed flight MH17 has compromised the most important step in victim identification and will likely lead to delays, a forensic expert says.
And it's possible that some victims may never be identified.
''It's heartbreaking,'' says Dr Kirsty Wright, a forensic biologist who headed DNA identification efforts in Thailand after the 2004 tsunami.
Tampering by rebels and locals, including the removal of bodies and the shifting of wreckage, has corrupted the crucial ''recovery phase''.
Ordinarily, this is the stage when scientists and police grid a disaster zone, take photos of bodies and belongings, collect evidence and - crucially - give everything a unique identification number.
This forms a ''chain of continuity'' which maintains the integrity of the forensic evidence and helps co-ordinate identification efforts.
''It takes thorough examination by people that know what they're looking for to make sure all of the wreckage is thoroughly searched and all the body parts are removed,'' she told AAP on Wednesday.
''If bodies or body parts are overlooked, quite simply they can't be identified.''
Refrigerated train carriages transporting the remains of Australian and other victims of MH17 arrived in the Ukrainian city of Kharkiv on Tuesday.
From there they will be flown to a barracks near the Dutch city of Eindhoven where forensic experts will begin identification efforts.
But Dutch investigators said not all the 298 victims have been recovered from the crash site, with 200 bodies or body parts aboard the train.
Wright said the treatment of bodies breached standard investigation protocol, which calls for a proper inventory of all victims.
She also said the debris field could be much larger than the reported 10 kilometres, citing the 9/11 attacks in New York, where body parts were found years later on the tops of buildings much further away from ground zero than investigators initially thought possible.
Under Interpol's disaster victim identification processes, three primary methods will be used to identify victims: fingerprinting, dental records, and DNA.
Fingerprinting and dental records can identify victims fairly quickly, but for fragmented or badly burned remains, lengthy DNA tests are often required.
''With any disaster when you have a large number of victims, there are some that get identified very quickly, within days or weeks,'' Wright said.
''Others are more difficult to identify. There's a bell-curve.''
Family members of many of the Australian victims have already provided DNA samples and other information to help with identification.
A team of forensic pathologists and dentists from the Victorian Institute of Forensic Medicine have flown to the Netherlands to assist.