It was a Virgin Australia pilot who first raised the alarm. At 9.58am on Friday Feb 21, the pilot intercepted a warning from the Chinese navy: a flotilla of warships were conducting live-fire drills in the Tasman Sea, some 300 nautical miles off the eastern coast of Australia.

The message – broadcast on the 121.5 MHz emergency radio channel used by commercial pilots to communicate – was relayed to the air traffic controller, who then passed it to the military.

“At that stage we didn’t know whether it was a potential hoax or real,” Peter Curran, deputy chief executive of Airservices Australia, told a parliamentary hearing this week.

But the message was not a hoax.

In a highly unusual move, three Chinese naval vessels dubbed Task Group 107 – including a Jiangkai-class frigate, a Renhai-class cruiser and a Fuchi-class replenishment vessel – were conducting exercises in Australia’s exclusive economic zone.

This area is beyond Australia’s territorial waters, but it has exclusive economic rights. To avoid any incidents, 49 flights were diverted.