Russian President Vladimir Putin has arrived in China for a three-day state visit set to be dominated by energy and trade issues.
Before setting off, Mr Putin said Russian interests would come first in deciding where to build a highly contested oil pipeline from Siberia.
Energy-hungry China and Japan have both been vying for Russia's oil.
The two Asian rivals have offered huge investments if their preferred pipeline route is picked by Moscow.
A pipeline to China would run about 2,400 kilometres (1,440 miles) from the Siberian city of Angarsk to the Daqing oil refineries in north-eastern China.
The estimated cost of the project stands at about $3bn dollars (2.4bn euros), but official figures vary.
The route favoured by Japan would cover some 4,100 km form the city of Taichet to the Sea of Japan port of Nakhodka.
It is estimated that this project would cost four times as much as the Chinese route.