China's foreign ministry said on Friday that it is "seriously" concerned about Japan's military and security moves, including ambiguity over its non-nuclear principles.

Japan's decision not to rule out acquiring nuclear submarines indicates a major "negative" policy shift, ministry spokesperson Lin Jian said at a press conference.

Japanese Prime Minister Sanae Takaichi this week hinted at a possible shift in the country's decades-old non-nuclear principles, raising speculation that she might seek to revise a ban on the entry of such weapons into its territory.