Imports from Russia reached 7.04 million tonnes, or 1.658 million barrels per day, in December, up 40 percent from 5.03 million tonnes a year earlier, according to the data from the General Administration of Customs.
For the full year, Russian imports rose to 71.49 million tonnes, or 1.43 million bpd, up 19.7 percent from 59.7 million tonnes in 2017.
Demand for Russian crude was supported by a rise in throughput by China's private refiners, who favour Russian grades such as ESPO, while geopolitical uncertainties also forced China to import less from countries such as Iran and Venezuela.
Russian oil giant Rosneft has also marketed its ESPO grade more aggressively, signing new long term supply deals with state oil companies such as ChemChina and PetroChina.
Saudi Arabia supplied China with 6.97 million tonnes in December, or 1.64 million bpd, up 48 percent from 4.71 million tonnes a year earlier.
For 2018, OPEC's top supplier boosted shipments to China by 8.7 percent to 56.73 million tonnes, or 1.135 million bpd.
That means Russia's lead over Saudi Arabia in supplying China almost doubled to 295,000 bpd in 2018 from 150,000 bpd a year earlier.
U.S. shipments to China — which have been hit by a trade war between the two countries — came in at zero in December. Imports for 2018 were up 24.8 percent from 2017 at 245,616 bpd.
Chinese oil trader Unipec plans to resume U.S. crude shipments to China by March, Reuters reported in December.