A Dutch air force transport plane carrying the first 16 coffins with the remains of victims of the downed Malaysian airliner took off on Wednesday from an airport in the eastern Ukrainian city of Kharkiv for the Netherlands.

Honorary guards placed wooden coffins on the plane after a short and sombre ceremony held on the tarmac before it took off.

Earlier, the black box flight recorders from the Malaysian airliner downed in eastern Ukraine arrived in Britain, the Ukrainian government's special investigation commission said.

"Today ... the black boxes from the airliner Boeing 777 arrived in Britain under the supervision of ICAO (International Civil Aviation Organization)," the commission said on its Facebook page.

All 298 people on board the Malaysia Airlines Boeing 777 perished when it was brought down last Thursday over rebel-held territory in eastern Ukraine, where Kiev is struggling to quell a pro-Russian separatist rebellion.

Many of the victims were Dutch and the Netherlands will carry out their identification.

At the ceremony, Ukrainian Deputy Prime Minister Volodymyr Groysman said the downing of the plane was an "inhumane terrorist act" carried out with help from Russia.

Kiev will do everything in its power to bring those guilty to justice, he added.

A Canadian military transport plane is due to leave Kharkiv with 24 more coffins later on Wednesday.

Meanwhile, Australian Prime Minister Tony Abbott said it was still unclear how many bodies from downed Malaysia Airlines Flight MH17 had arrived in the Ukrainian city of Kharkiv and how many may have been left behind at the crash site.

Five refrigerated wagons containing 200 body bags reached Kharkiv on Tuesday after pro-Russian separatists agreed to hand over the plane's black boxes to Malaysian authorities and the bodies to the Netherlands, where many victims had lived.

Abbott said that based on an initial inspection of the remains in the train carriages, that it was unclear how many bodies may still be left behind in rebel-held territory.

"Based on early inspection of the trains in Kharkiv, we just don't know how many bodies we have," Abbott told reporters.

"It's 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. That is the predicament in which we find ourselves."

The Boeing 777 was shot down last week in eastern Ukraine en route from Amsterdam to Kuala Lumpur, killing all 298 passengers and crew on board. Twenty eight Australians were killed. - Reuters