The Chinese naval exercises, in international waters off Australia’s eastern coast, while legal, have nonetheless sparked alarm in Australia and New Zealand.

Commercial airliners flying over the Tasman Sea between Australia and New Zealand were forced to reroute their flights on Friday morning Australian time because of a People’s Liberation Army Navy (PLAN) action group warning that it would conduct live-fire drills.

Airlines have been contacted by Australia’s air traffic control agency warning them of reports of live fire off the country’s east coast where a Chinese navy task group has been operating, the agency and Australian officials said.

Australia and New Zealand are monitoring a group of Chinese naval vessels spotted in international waters near Sydney, the countries’ defence ministers said on Thursday. Three Chinese vessels are traveling down the eastern coast of Australia,

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