The letter, sent via the Chinese embassy in Japan, stressed the need to “fight protectionism together”, Kyodo said, citing multiple Japanese government officials.

The foreign ministries of both countries did not immediately respond to a request for comment.

Yesterday, Beijing warned countries against striking a broader economic deal with the US at its expense, ratcheting up its rhetoric in a spiralling trade war between the world’s two biggest economies.

Japan, one of Washington’s closest allies, was among dozens of countries targeted by Trump’s sweeping tariffs earlier this month and has begun negotiations with the US to try and resolve the issue.

Relations between Beijing and Tokyo have been strained in recent years by a range of issues, from territorial disputes to trade tensions.