Prime Minister Tony Abbott is discussing with government leaders options for securing the 50-square kilometer (20-square mile) crash site, including his preferred option of a multinational security force mounted by countries such as Australia, Netherlands and Malaysia that lost citizens in the disaster.
''My fear is that unless we do more ... some of them will never come home,'' Abbott told reporters, referring to the 37 Australian citizens and residents who were killed.
''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 said.
A refrigerated train carrying human remains reached the Ukrainian government-controlled town of Kharkiv late Tuesday, but it was not possible to tell from initial inspections how many of the 298 victims were aboard, Abbott said.
He said Australian and Dutch aircraft would begin flying remains from Kharkiv to the Netherlands late Wednesday for identification.
Abbott said his special envoy in Kharkiv, former Australian defense force chief Angus Houston, had reported that an international search of the entire debris field which covers farms and villages is essential.
''In his view, we need a large team conducting a forensic search - a proper scouring of the site to identify anything that may have been missed up until now because it's entirely possible, in his view, that there could be further human remains or further significant wreckage in the area,'' Abbott said.
''Such a forensic search can only happen if the area is secure. Of course, it's normal in circumstances such as this for a cordon to be established that is off limits to anyone except investigators,'' he added.
Abbott declined to say whether farmers and villagers within the area should be kept out.
''We're talking about doing what's reasonably necessary to conduct a full forensic search, a full and thorough investigation and to ensure that as far as is reasonably possible we bring them home - not just some of them, but all of them,'' Abbott said.
Australia sponsored a U.N. Security Council resolution passed unanimously on Monday demanding that rebels who hold the crash site cooperate with an independent investigation and allow victims' remains to be recovered.