The Pentagon says a Chinese fighter jet conducted a "dangerous intercept" of a U.S. Navy aircraft three days ago off the coast of China in international airspace.

The Pentagon press secretary, Rear Adm. John Kirby, said Friday that Washington has lodged a protest to China through diplomatic channels.

Kirby said the Chinese jet made several close passes by the Navy P-8 Poseidon plane, coming within 10 metres of it. He said the Chinese jet did a roll manoeuvre over the top of the Poseidon and also passed across the nose of the Navy plane, exposing the belly of the fighter in a way apparently designed to show that it was armed.

Kirby said it happened about 215 kilometres east of Hainan Island.