The flight by two Russian Tu-95 strategic bombers and two Chinese H-6 bombers, backed up by a Russian A-50 early warning plane and its Chinese counterpart, a KJ-2000, marks a notable ramping-up of military cooperation between Beijing and Moscow.

That is something likely to worry politicians from Washington to Tokyo and could complicate relations and raise tension in a region that has for years been overshadowed by hostility between the United States and North Korea.

While troops and naval ships from Russia and China have taken part in joint war games before, they have not, according to Russia's Ministry of Defence, conducted such air patrols in the Asia-Pacific region together until Tuesday.