Monday was the second day in a row that fighting prevented  Australian investigators from getting to the MH17 crash site.

About mid-morning their convoy headed away from the Radisson Park Inn in Donetsk, but it got no further than Shakhtersk, 12km from the crash site, when heavy shelling forced it to retreat to Donetsk.

It appeared that only two of the 11-man AFP team now in Donetsk was in the convoy, which was led by conflict monitors from the Organisation for Security and Cooperation in Europe.

Heavy shelling could be heard from where the convoy came to a halt. A decision has yet to be made on whether to abort or to sit out the violence by the road.

The visit comes as  a Ukrainian security spokesman says the data from the recovered flight data recorders shows the Malaysia Airlines flight crashed due to a massive, explosive loss of pressure after being punctured multiple times by shrapnel.

National security spokesman Andriy Lysenko said on Monday the plane suffered "massive explosive decompression" after it was hit by fragments he said came from a missile. The data recorders were sent to experts in Britain for examination.

The Organisation for Security and Cooperation in Europe had approved the visit by the Dutch-led police mission.

The 49-member Dutch-Australian police team cancelled its first attempt to access the crash site near Donetsk on Sunday as forces loyal to the Kiev government stepped up their attack on Russian-backed rebels in the region.

Late on Monday night Australian time, Ms Bishop said from Kiev that she and her Dutch counterpart, Frans Timmermans, had met OSCE representatives and that "we were informed that the conditions were such that our convoy could leave Donetsk and head towards the crash site and so our understanding is that the convoy is under way".

"We are here for one purpose, and that is to ensure that the site is secured to enable us each day to scour it for remains of those aboard MH 17 and to commence the crash site investigation,'' she said.

Ms Bishop said that a humanitarian corridor would be established to ensure regular access to the site and that a number of check points had been established on the route from Donetsk.

Some were controlled by the separatists and some by the Ukrainian military, she said, but said it was understood the crash site was still controlled by militants.

Ms Bishop said she and Mr Timmermans would meet President Poroshenko and other Ukrainian politicians overnight on Monday to seek assurances the Ukrainian military action did not compromise the search effort and abided by the UN Security Council resolution that called for a ceasefire.

In a subsequent interview on the ABC's 7.30, Ms Bishop said the situation on the ground near the crash site was fluid, with the Ukrainian government taking more ground in the past 24 hours.

She said ADF personnel were playing a part in providing logistics and support but stressed that unarmed police were headed to the crash site.

"The agreement we have struck with the Ukrainian government, that is in a document I signed last Friday morning and the Dutch are about to sign a similar document with the Ukrainian government does allow for the contingency of armed personnel should that be required,'' she said.

"That's why the agreement does need to go to the parliament."

Ms Bishop overnight on Monday reiterated Australia's determination to get to the crash site, despite it still being in the hands of separatists.

''We will do it again tomorrow, the same way until we can get to the crash site,'' she said.

''Everyday we will assess the situation, we will assess the operational risk and decide whether to proceed or not.''

Ms Bishop said while police officers would not be put in ''harm's way'', Australia will continue its efforts to try and ''retrieve the bodies of Australians''.

A spokesperson for the Prime Minister Tony Abbott said on Tuesday that the security situation in the area around the crash site ''remains highly volatile'' and the ''risks are real''.

Earlier on Monday, deputy federal police commissioner Andrew Colvin admitted his discomfort with his officers being unarmed in the contested territory.

He also warned the remains of some of the 298 people, including 38 Australian residents, killed in the disaster may never be recovered as he noted the possibility of evidence being lost as fighting intensified.

Dutch Prime Minister Mark Rutte, whose country is leading the investigation, has put a three-week time limit on the repatriation effort from Sunday.

Mr Colvin said that after assessing the risks, he believed it was safe to send AFP officers into the crash site though he was not comfortable with the security situation.

''Comfortable is a broad word, no we can't be comfortable but we have . . . dealt with the risks to a point where we wouldn't send our people into a situation where we didn't think they would be safe,'' he said.

Mr Colvin said while the AFP had responded to disasters, terrorist attacks and conflicts in the past, they had never done so without weapons.

''We haven't deployed in a conflict zone in this manner before,'' he said.

''We've said all along that this is a risky mission but we are working on the basis that if it's a permissive environment we will go in, if it's a permissive environment those risks are reduced.

''We have to prepare ourselves for the possibility that not all remains will ultimately be recovered.''

Mr Colvin revealed the the AFP was in direct contact with the rebels through Organisation for Security and Co-operation in Europe intermediaries and believed the multinational team was ''welcome'' at the site but had to wait until it was safe on the ground.

''We'd have to be satisfied that whoever holds the ground holds it in a manner that they can assure our safety.

''We need perspective on what that welcome looks like but this is a contested zone so there is active fighting going on.''

The government has stressed the mission is a humanitarian one, however, the multinational team, consisting of 11 AFP officers and 38 Dutch officials, will also try and recover any wreckage they believe will assist official investigators.

In Holland, the first remains of a Dutch victim of the downed flight have been identified by forensics.

An extraordinary session of the Ukrainian parliament will be held on July 31 to discuss the international response to the crash.

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