Chinese warships have travelled across the Tasman Sea and were more than 500km west of Hobart, on the edge of Australia's exclusive economic zone as of Thursday.
The vessels are being surveilled by Australian ship HMAS Stuart as it tracks towards the Great Australian Bight with the possibility they are circumnavigating Australia, Mr Marles said.
But concerns have been raised the Australian military only learned about firing drills after the training window opened.
Also drawing scrutiny is that Australia was first alerted by a Virgin pilot who heard the emergency broadcast mid-flight and not the New Zealand navy tracking the ship.
Defence was notified by aviation officials by 10.10am on Friday, 40 minutes after the window opened, followed by New Zealand about 11am.
Mr Marles defended the time lag in the notification by New Zealand of the window opening for live-fire drills, saying he did not believe there was an issue with the time frame.
"In respect of the communication between New Zealand and Australia, we're totally happy with that," he said on Friday.
But it's unclear whether a live firing took place, Mr Marles said.
"The New Zealand frigate which we were working closely with, which was the frigate that was observing the task group at the time, didn't observe any live firing on that day," he said.
Asked if it would be alright for New Zealand to take 90 minutes to inform Australia of a threat, Mr Marles said it wasn't fair to conflate the two issues.
"We are surveilling that exercise and that is a very different circumstance to the country being under threat," he said.
"It's really important that we take a deep breath here."
While maintaining the Chinese ships were acting in accordance with international law because they are allowed to be there, Australia says the notice given was inadequate and representations have been made to Beijing, including at the foreign minister level.
The Australian Defence Force provides up to 48 hours' notice of live-fire activities by issuing a notice to airmen, but the timing depends on a range of operational factors and this can shorten to between 12 and 24 hours, Foreign Affairs Department deputy secretary Elly Lawson advised a Senate committee.
Opposition home affairs spokesman James Paterson questioned why Australia could not determine on its own whether a live firing drill took place.
"I am concerned about a series of national security breakdowns here," he said.
"If our Chinese friends didn't tell us, we should use our own intelligence and defence assets to get on top of this issue and it's a great concern to me that we didn't."
It's also unknown whether a Chinese submarine accompanies the ships, Mr Marles said, with it not unusual for one to join such a task force.
He defended the startling admission, which first came from Chief of the Defence Force Admiral David Johnston, saying this was why Australia's acquisition of nuclear-powered submarines mattered.
"We can't answer that question definitively, which is precisely why it's important that Australia has a long-range submarine capability," he said.
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