It comes as Member for Bendigo Lisa Chesters urged the government to order replacement vehicles from Thales Australia's Finn Street factory.

"We can't leave the Australian army under-resourced," the opposition MP said.

Defence spent the early hours of Friday working on options after Ukraine president Volodymyr Zelenskyy made the request to Australia's parliament.

Discussions were still going on behind closed doors when defence representatives mistakenly told a senate estimates committee Australia had agreed to send "up to four" Bushmasters.

The number prompted an exasperated Labor senator Penny Wong to ask "is that all we can do?"

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Defence has close to 1000 Bushmasters.

The brief confusion was triggered by comments defence minister Peter Dutton had just made in a media interview with Sky News.

He had been discussing the possibility of adding Bushmasters C-17 military plane supply flight already in the works.

"We might only be able to upload three or four Bushmasters on to a C-17 at once," Mr Dutton said during the interview.

"But we're just going through that logistics at the moment. So we're very much open to whatever support we can."

Bushmasters are not the only Bendigo-based military vehicle that could be shipped to Ukraine.

Ms Chesters said she was pushing for Hawkeis to be considered too. Thales also builds those armoured vehicles in Bendigo.

They can withstand bomb blasts but are light enough to be lifted by some helicopters.

"They are lighter and they might be easier to get to the conflict in Europe than shipping Bushmasters from Australia," Ms Chesters said.

Ukraine had not raised Hawkeis in its requests but defence chief Angus Campbell told the senate committee a range of ideas are being considered.

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"We may get to Hawkeis. Not at this stage," he said.

The army has so far paid for 400 of Hawkeis that are sitting idle in Bendigo, in central Victoria.

It wants some extra work done on them to meet its standards before they enter Australian military service.

Even with that uncertainty, Ms Chesters said Hawkeis had the potential to be important parts of the Ukraine response.

"We don't know how long this conflict is going to go on. Yes, [Ukraine wants] vehicles immediately, but they also might need them next month or the one after," she said.

"We need to be there supporting Ukraine until the end."