A ceasefire agreed between Ukrainian forces and pro-Russian rebels has come into force, the first step in a fragile peace plan aimed at ending 10 months of conflict in east Ukraine.

The truce officially started at midnight Ukraine time (0900 AEDT Sunday), but surging fighting in the run-up to the ceasefire has already cast doubt on whether it will be respected.

Under the terms of the deal, inked on Thursday after marathon talks in Minsk between the leaders of Ukraine, Russia, Germany and France, the two warring sides have two days from the start of the truce to start pulling back heavy weapons from the frontline.

The last-ditch peace plan is seen as the best hope of ending the violence that has claimed at least 5480 lives since April but scepticism remains high after the collapse of a similar previous deal.

Ferocious fighting raged in the hours before the ceasefire was set to come into effect, with Ukraine and the United States accusing Russia of piling in weapons to fuel a rebel onslaught to grab territory.

German Foreign Minister Frank-Walter Steinmeier warned on Saturday of dire consequences for Europe if the Ukraine ceasefire fails.