Seventy police investigators - by far the largest number to reach the location so far - were conducting "search operations in several places at the crash site," a Dutch government statement said.
The mission is tasked with launching an international probe into the downing two weeks ago of the Malaysia Airlines plane with the loss of all 298 people on board.
Over 200 coffins have been sent back to the Netherlands, which lost 193 citizens in the July 17 crash, but many remains have yet to be recovered because of the fighting. "If they find human remains while searching, they will immediately be recovered," said Pieter-Jaap Aalbersberg, the Dutch police official sent to Ukraine to head up the mission.
Fighting and rebel restrictions to the site next to the town of Grabove had prevented the investigation getting under way before now, and the conflict was still raging today.
70 investigators were conducting "search operations at the crash site"
The Ukrainian military said an overnight ambush by insurgents in Shakhtarsk, a town 25 kilometres from the main impact site, left 14 people dead, including at least 10 soldiers. The clash broke a brief lull that had reigned around the site after Ukrainian authorities ordered a ceasefire.
"In total it is known that 14 people died but the bodies of four of them have not been identified and could be Ukrainian soldiers or terrorists," military spokesman Oleksiy Dmytrashkivsky told AFP. Another spokesman said 13 soldiers were injured and 11 were still missing as clashes continued.
An AFP team some 12 kilometres from the MH17 site heard the sound of tank fire and saw smoke rising from the direction of Shakhtarsk. Both rebels and Kiev have vowed to secure a circuitous access corridor to the location traced by scouts from the international team yesterday.
Ukraine's army has pledged not to fight in the immediate vicinity of the insurgent-held site.