Chinese warships conducting exercises off Australia’s east coast issued surprise warnings to airliners over the Tasman Sea, alerting them to a live-fire drill.

Australian authorities, unaware of the exercise, only learned about it from commercial pilots.

Flights from Sydney to New Zealand diverted but were not in danger.

Australian officials criticized China for the lack of prior notice, while China defended the drill as legal and in line with international law, the Associated Press has reported.

The incident highlights China’s expanding naval presence in the region.

Written by B.C. Begley