Chinese warships have undertaken an apparent live-fire drill in the seas between Australia and New Zealand, diverting commercial flights in the skies above.

The Chinese navynotified the Australian defence department shortly before the drill on Friday.

Three People’s Liberation Army-Navy vessels – the Jiangkai-class frigate Hengyang, the Renhai-class cruiser Zunyiand theFuchi-class replenishment vessel Weishanhu – are now about 340 nautical miles off Eden, on the New South Wales south coast, in international waters. The drill was conducted in international waters and in accordance with international law.

It is understood at least three commercial flights diverted their course.

The three Chinese naval ships – known as Taskgroup 107 – advised Australia early on Friday of plans to conduct a live-fire exercise.

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The flotilla was being shadowed by a NZ navy vessel, which observed the drill. The ships changed formation and placed a target in the water, manoeuvred again, and then recovered the target. No live fire was observed, but the change in formation was consistent with a live-fire drill.

It is understood there was no surface-to-air firing.

Australia has asked China – through defence attaches in Canberra and Beijing – for more information on the live-fire drill and plans for any further exercises.

It is understood the drill, conducted at short notice, is being viewed within the Australian military as a “significant disruption” but not one that posed an elevated risk to airspace users.

Anthony Albanese said China had issued an alert that it would be conducting the activities, including the potential use of live fire.

“It’s outside of Australia’s exclusive economic zone,” he said. “Australia and New Zealand ships and aircraft have been monitoring the Chinese fleet while they have been travelling down the coast of Australia off the coast, as you would expect us to be doing.”

Asked what his level of concern was, Albanese said the activity was consistent with international law and the Chinese had given warning.

The shadow minister for defence, Andrew Hastie, accused the Chinese government of using “gunboat diplomacy”, blaming the “latest provocation” on weakness from the prime minister.

“For two and a half years, Anthony Albanese and Richard Marles have refused to stand up for our ADF personnel,” he said.

“The Australian people deserve to know what is going on, and they deserve better leadership from our weak prime minister.”

The foreign minister, Penny Wong, told ABC television the Chinese ships’ presence in waters off Australia was an evolving situation, but she believed live-fire exercises had been conducted.

“We will be discussing this with the Chinese, and we already have at official level, in relation to the notice given and the transparency provided in relation to these exercises, particularly the live fire exercises,” Wong said.

She said Australian military was monitoring the Chinese task group “very closely”, but acknowledged it was operating in international waters.

Wong, in Johannesburg for a meeting of G20 meeting of foreign ministers, is expected to meet with her Chinese counterpart, Wang Yi, on the sidelines of the conference Friday night.

Airservices Australia has been providing advice directly to pilots in the area by radio.

“The Civil Aviation Authority (CASA) and Airservices Australia are aware of reports of live firing in international waters,” a spokesperson said.

“As a precaution, we have advised airlines with flights planned in the area. We are also working together to coordinate advice to operators and pilots.”

The airspace protection zone – 18km around the Chinese vessels and up to 45,000ft – remains current.

According to earlier Chinese media reports, the PLA-Navy frigate, cruiser and replenishment vessel have been conducting “real-combat” exercises in an unspecified part of the Pacific Ocean over the past month.

The ships’ presence off Australia’s coast closely follows an incident in the South China Sea last week in which a Chinese fighter jet released flares in front of an Australian military plane.

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