Dutch experts supervised a crew from the emergency ministry of the self-proclaimed Donetsk People's Republic as they began cutting pieces of the plane's wreckage with metal saws at the crash site near the village of Grabove, an AFP reporter at the scene said.
Investigators from the Netherlands heading the probe into the disaster, in which 193 Dutch citizens died on a flight from Amsterdam to Kuala Lumpur in July, said it could take "several days".
The investigation team said the wreckage would be collected before being transported to the Ukrainian government-controlled city of Kharkiv and then flown to the Netherlands.
The Dutch experts eventually intend to reconstruct a section of the doomed airliner.
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A rebel official said they hoped to finish the operations in the next ten days and that work would start on the largest chunks of fuselage first.
The team faces a race against time to complete the recovery effort before harsh winter conditions in the former Soviet state make it difficult to continue.
Ukraine and the West accuse Russia of supplying pro-Moscow rebels with the missile that shot down the Boeing 777 in an incident that stepped up international pressure on Moscow over its role in the conflict in Ukraine.
Moscow and the separatists have strenuously denied they were behind the downing of the plane, pointing the finger of blame instead at Kiev.
After a series of frosty exchanges with his fellow leaders, Putin left the summit ahead of schedule today, saying he needed to catch up on some sleep.
The MH17 probe team has so far managed to collect and identify the remains of 289 victims from the tragedy but recovery operations have been disrupted by fierce fighting in the area between government forces and insurgents.