Two senior transport safety investigators flew out from Canberra on Monday morning on their way to the Ukrainian capital Kiev.

ATSB chief commissioner Martin Dolan assured Australians the bureau would offer maximum resources to the international investigation team.

“These investigations do take time because they need to be thorough and they require the examination of a whole range of different aspects," Mr Dolan said.

"We normally say, as investigators, it can take up to a year to get a firm result so it’s quite possible there will be no quick response."

Although access to the crash site has been limited, an international team of investigators, officially coordinated by the Ukrainian government, has gathered to assist when the crash site is deemed safe.

“What we have is assurance that there is a team being formed in Kiev and all possible steps are being taken to ensure that team gets access to understand the source of this tragedy,'' Mr Dolan said.

"[The situation] is still somewhat in flux, but it’s very important that we have people on the ground ready to go when the access to the site is guaranteed, and we hope it will happen soon.''

Armed rebels have reportedly forced emergency service workers to hand over the bodies from the crash site and removed them to an unknown location.

Senior transport safety investigator Paul Ballard said the team needed to prepare for a very different situation than if it were not in a war zone.

“[The way the site has been treated] always makes it more difficult for us. Every site tends to be different," he said.

"We've got to understand that this isn't a site within Australia, so it will get treated in the manner is does in those countries, and this is a more difficult situation as this is a less controlled site than we’re used to."

The ATSB will deploy more resources if deemed necessary.