Sailing in Australia’s exclusive economic zone, the three vessels were not breaking international law, but they were unusually far south on an undeclared mission.

Three Chinese warships have been spotted in international waters off the coast of Australia’s largest city, Sydney, in a rare show of military might that will likely test diplomatic ties between Canberra and Beijing.

The Australian and New Zealand militaries are monitoring three Chinese warships that are moving unusually far south along Australia’s east coast on an unknown mission

The vessels were sailing in the Tasman Sea, and their announced intent to perform exercises prompted a call for commercial flights to divert course.

China did not formally inform the Defence its three warships off Australian waters were to undertake live fire testing, which forced a warning to commercial flights in the area.

The Australian navy is shadowing Chinese warships 150 nautical miles east of Sydney, the furthest China’s navy has sailed down the eastern Australian coast. Two Australian ships are following a Chinese naval task group — comprising two warships and a supply vessel — that appeared off the north-eastern coast of Australia a week ago,

Defence Minister Richard Marles said the vessels did not pose any threats but their presence was an ‘unusual event’.

Australian officials said the ships were "off the east coast of Australia" and their presence there was unusual.

Several commercial flights have been re-routed because of potential hazards from Chinese warship exercises between Australia and New Zealand.