China claims almost all of the South China Sea, despite an international ruling in 2016 concluding its claims have no legal basis.

On Friday, US President Donald Trump and Japanese Prime Minister Shigeru Ishiba said they opposed China's "unlawful maritime claims, militarisation of reclaimed features, and threatening and provocative activities in the South China Sea" in a joint statement after they met in Washington.

Chinese foreign ministry spokesman Guo Jiakun hit back on Monday, saying "the China-related content of the US-Japan joint statement blatantly interferes in China's internal affairs, attacks and smears China and exaggerates regional tensions".

China had "lodged solemn representations" with both countries, he added at a regular press briefing.

Beijing has in recent months pressed its territorial claims in the South China Sea more stridently.

Its claims overlap with Malaysia, Vietnam, Indonesia, Brunei, and the Philippines.