In public, President Vladimir V. Putin of Russia says his country’s growing friendship with China is unshakable — a strategic military and economic collaboration that has entered a golden era.

But in the corridors of Lubyanka, the headquarters of Russia’s domestic security agency, known as the F.S.B., a secretive intelligence unit refers to the Chinese as “the enemy.”

This unit, which has not previously been disclosed, has warned that China is a serious threat to Russian security. Its officers say that Beijing is increasingly trying to recruit Russian spies and get its hands on sensitive military technology, at times by luring disaffected Russian scientists.

The intelligence officers say that China is spying on the Russian military’s operations in Ukraine to learn about Western weapons and warfare. They fear that Chinese academics are laying the groundwork to make claims on Russian territory. And they have warned that Chinese intelligence agents are carrying out espionage in the Arctic using mining firms and university research centers as cover.

The threats are laid out in an eight-page internal F.S.B. planning document, obtained by The New York Times, that sets priorities for fending off Chinese espionage. The document is undated, raising the possibility that it is a draft, though it appears from context to have been written in late 2023 or early 2024.