It's one of a long list of things I've heard and never looked into, but apparently large areas of land in Russia, mainly in the east, have been given over to Chinese control, they clear the forest / extract the water / wreck the soil with some kind of short-term intensive farming / pollute the fuck out of it / cover it with greenhouses and send the food back to China etc. In that case I mean the land is still Russian, but is under full control of a Chinese company and lots of Chinese move there, for a while anyway.
I've actually heard some borderland has been given over to become part of China as well, and there are plans for China to take over the eastern third of half of Russia. It's all going on quietly apparently.
Russia does have a lot of nukes, so it could physically stop China if it wanted, but both countries are under the control of the same people at the top level I think.