The prime minister confirmed in March that a $10 billion base would be built on Australia's east coast as part of the AUKUS partnership with the US and UK.

Port Kembla has been touted as the base's preferred home, with the shortlist also including Newcastle and Brisbane.

However, Green's Gilmore candidate Carmel McCallum believed Jervis Bay hasn't been entirely ruled out as an option, given that a 2011 Defence report had not backed the shortlisted sites as preferred locations.

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The 2011 review ranked two Jervis Bay sites as favoured sites for a subs base, followed by Sydney Harbour.

"We don't need a $10 billion nuclear submarine base scarring the national park in our beautiful Jervis Bay," Mrs McCallum said.

"Scott Morrison must come to Gilmore and rule out a nuclear submarine base going anywhere in Australia, let alone Jervis Bay, because we simply cannot believe his earlier announcement."

The prime minister visited Sikorsky Australia's manufacturing site at Nowra on Monday, alongside Liberal candidate Andrew Constance, to announce a $2.5 billion helicopter fleet expansion for HMAS Albatross.

After he inspected a Seahawk helicopter, Mr Morrison took a question from the Register on whether he could rule out Jervis Bay as a location for a nuclear submarine base.

He responded simply: "I can."

"It's not one of the shortlisted sites. It's not one of the shortlisted sites, at all," Mr Morrison said.

Jervis Bay was discounted as a feasible option for subs base due to it being a marine park, according to the Department of Defence.

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Despite Mr Morrison's answer, Mrs McCallum maintains her suspicions that the Coalition could still choose Jervis Bay.

"If the prime minister lied to the French president, why would the people of Gilmore believe anything that comes out of his mouth?" she said.

"That report done in 2011 looked at every aspect, from where families would like to live, how hard it is to get to a place with traffic, how deep the water is.

"(Jervis Bay) ticks all the boxes, sadly."

The federal opposition supports the AUKUS partnership, but Labor's incumbent Gilmore MP, Fiona Phillips, said she wouldn't put it past the Coalition to choose Jervis Bay for a subs base.

"I wouldn't rule anything out from the Morrison Government," Mrs Phillips said.

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When Port Kembla was announced as a shortlisted site, it sparked mixed reactions for what it may mean further south.

Some leaders viewed it as a jobs opportunity for the Shoalhaven, and others believed it would place a target on the region.

Defence had looked at 19 potential sites for a subs base and narrowed them down to the three preferred locations.

Defence would discuss the plans further with state and local governments and "begin negotiations on what will be an enormous undertaking".

The moves come amid uncertainty about when the first of the nuclear-powered submarines will be operating as part of the agreement.

Morrison originally expected it would be by 2040 but the government insists it may be sooner.

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