Dozens of commercial flights had to change course last week when they were surprised by Chinese naval drills off the coast of Australia. But China said its navy repeatedly issued notices.

Some 49 commercial flights were forced to change course last Friday when Chinese warships unexpectedly announced naval drills off the eastern coast of Australia, officials said in a government hearing.

Three warships conducted a series of live-fire drills on Friday and Saturday, right under a busy flight path connecting Australia and New Zealand.

What do we know about the Chinese drills?

A Virgin Australia commercial flight first picked up the broadcast from the Chinese warships and alerted the country’s air safety agency on Friday morning.

“At that stage we didn’t know if it was a potential hoax or real,” Air Services Australia deputy chief executive Peter Curran told a government hearing on Monday evening.

Curran said the broadcast was over a channel monitored by pilots. “It’s an international guard frequency. Air traffic control does not monitor that frequency but pilots do. So we can’t hear what was said.”

Of the 49 flights, some were en route when the air safety agency learned of the drills and confirmed their legitimacy, Curran added. In addition to Virgin Australia, flights operated Qantas, Air New Zealand and Emirates also modified their flight path.

While the exercise took place in international waters, Australia and New Zealand have criticized Beijing for running the drills without due warning.

What has China said about the matter?

China has defended its conduct as “safe, standard and professional”.

On Saturday, Canberra had said it did not get a satisfactory explanation from Beijing about Friday’s drill.

China’s Defense Ministry responded on Sunday saying the remarks of the Australian government were “completely inconsistent with facts” and that Beijing had conducted drills after “repeatedly issuing prior safety notices.”

“Australia, while well aware of this, made unreasonable accusations against China and deliberately hyped it up,” said Chinese Defense Ministry spokesperson Wu Qian.

He added that Beijing was “astonished and strongly dissatisfied”.

The incident comes within a month of Canberra accusing Beijing of “unsafe” military conduct after the latter’s fighter jet dropped flares near an Australian air force plane patrolling the South China Sea. Beijing has said the Australian plane was intruding in the airspace without China’s permission.