Moscow and Beijing have reached agreement on a $60 billion contract to ramp up Russian oil supplies to China, part of the two countries' strategy to tighten their energy partnership, Russian President Vladimir Putin said on Thursday.

"A contract with Rosneft company has been prepared which is large-scale and unprecedented without any exaggeration," Putin told Chinese Vice Premier Zhang Gaoli at a meeting in Saint Petersburg, estimating the value of the deal at more than $60 billion.

In his comments open to the media, Putin did not say when the firm contract would be signed.

A preliminary agreement to gradually raise Russian oil supplies to China over the next 25 years from their current level of 15 million tonnes per year was reached during China's leader Xi Jinping's visit to Moscow in March.

As part of the deal, Russian oil state company Rosneft is to receive a $2 billion loan from China.

Russia, which wants to diversify its energy customers away from Europe, also needs to finalise a potentially huge gas deal with China but a commercial contract has so far proved elusive as talks have become mired in pricing disputes.