Defence conducted a review of the security implications of the port's 99-year leasing arrangement with China's Landbridge Group but found no national security grounds to recommend the federal government overturn the deal.

Infrastructure Minister Barnaby Joyce has flagged $1.5 billion for "new port infrastructure" in Darwin, with the ABC saying it understands the funds refer to a new port to be announced during the upcoming election campaign.

Mr Dutton did not rule out the possibility of a new Darwin port when pushed by reporters on Thursday.

"There's a massive commitment from the government into the Northern Territory and that does look at port development and ways in which we might be able to look at support through contracts in defence for example," Mr Dutton said in Canberra on Thursday.

"We will have more to say about that in due course."

But the first assistant secretary of the national security division in the prime minister's department told a Senate hearing it was his understanding the money was for modifications to the existing port.

"It's a facility within the existing port is what's been described," Lachlan Colquhoun said.

"There's $1.5 billion for new port infrastructure such as a new wharf and offloading facility, dredging of the ship and dredging of the shipping channel to boost the region's importing and exporting ability."

Finance Minister Simon Birmingham also appeared to walk back some of the speculation, telling reporters there were new infrastructure measures across the country, including in relation to the port.

"That includes particular investments just outside of Darwin, supporting an industrial precinct there that has huge opportunity to be a growth engine for the territory economy and a wealth generator for Australia," he said.

Senator Birmingham also suggested the government would overrule any similar leases.

"It was not a sale subject to Commonwealth government approval at the time. If it happened today - thanks to the changes our government made to Australia's foreign investment laws - it would be subject to direct approval.

"I would suspect it will not receive that approval."

Prime Minister Scott Morrison previously said the federal government would only act in relation to the port lease "if there is advice from the Defence Department or our security agencies that change their view about the national security implications of any piece of critical infrastructure".

Australian Associated Press