New Zealand’s defence minister has warned that Chinese warships located off the east coast of Australia are armed with “extremely capable” weapons that could reach Australia.

The three vessels, known as Taskgroup 107, undertook two live-fire exercises in the seas between Australia and New Zealand last week, causing commercial flights to be diverted in the skies above.

Judith Collins, the defence minister of New Zealand, said on Monday that the ships were currently 280 nautical miles (518km) east of Tasmania and were being closely monitored by New Zealand navy vessel Te Kaha.

Collins said the presence of the vessels in waters off New Zealand and Australia, and the short warning given by the Chinese government before the live-fire exercise on Friday was “unusual”.

“We’ve certainly never seen a task group of this capability undertaking this sort of work, it’s certainly a change,” she told RNZ Radio.

“The weapons they have are extremely capable. One has 112 vertical launch cells and has reported anti-ship ballistic missile range of 540 nautical miles,” she said.

Collins said the information she had was that the vessels were not nuclear-powered and did not have nuclear weapons, or missiles capable of carrying a nuclear warhead, onboard.

“They’re not telling us what they’re planning,” Collins told RNZ. “We’re taking them at face value that they are undertaking normal transits when it comes to the UN Convention on the Law of the Sea, that they’re not breaking the law.

“But as we’ve said, it is always better to give a lot more notice when it comes to live firing.”

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

Collins told RNZ that assertions by China’s ambassador to New Zealand that appropriate advance notice of the drills had been given were “wrong”.

“There was a warning to civil aviation flights, that was basically a very short amount of notice, rather than what we would consider best practice which is 12-24 hours notice, so that aircraft don’t have to be diverted when they’re on the wing.”

On Friday, the first live-fire exercise was observed by a New Zealand navy vessel. It involved the ships changing formation and placing a target in the water, manoeuvring again, and then recovering the target. No live fire was observed, but the change in formation was consistent with a live-fire drill.

On Saturday, New Zealand navy personnel advised live rounds were fired from a Chinese warship in international waters.

Australia’s prime minister, Anthony Albanese, said on the weekend that senior defence officials were continuing to monitor the ships after they were first spotted moving south in international waters about 280km off Sydney on Thursday.

The foreign affairs minister, Penny Wong, met with her Chinese counterpart and demanded to know why the vessels only offered limited notice before the firing was carried out.

China’s actions are believed to have complied with international law and the Australian Defence Force advised there was no imminent threat to its assets or those of New Zealand.