A Chinese company has won the bid to operate the Port of Darwin under a 99-year lease deal worth $506 million, NT Chief Minister Adam Giles has announced.

Mr Giles announced the Port of Darwin will have a new operator under an agreement signed today with the Landbridge Group worth $506 million, in a deal he described as "a fantastic outcome for the Territory".

Under the terms of the agreement, Mr Giles said the Territory would lease the Darwin Port land and facilities of East Arm Wharf, including the Darwin Marine Supply Base, and Fort Hill Wharf to the Chinese-owned Landbridge Group for 99 years.

The Territory will retain Stokes Hill Wharf, Fisherman's and Hornibrook's Wharves and Frances Bay facilities.

As part of the deal Landbridge have paid the full price for the lease, but only taken an 80 per cent ownership stake, Mr Giles said.

Within five years the Chinese company must find an Australian investor to purchase the other 20 per cent, and until that time that stake will remain with the NT Government.

Mr Giles said this kept a promise he had made for a large element of the port to remain in Australian hands.

Key points: Chinese company Landbridge to pay $506 million for 99-year lease

Chinese company Landbridge to pay $506 million for 99-year lease Landbridge has 80 per cent stake and must find Australian investor to pick up remainder

Landbridge has 80 per cent stake and must find Australian investor to pick up remainder Landbridge says no forced redundancies at least until 2018

Landbridge says no forced redundancies at least until 2018 Lease deal slammed by Maritime Workers Union

Lease deal slammed by Maritime Workers Union NT Labor condemns deal but says "we must honour contract"

NT Labor condemns deal but says "we must honour contract" Landbridge is owned by Chinese billionaire Ye Cheng

He said in Landbridge, the NT had "a partner that has demonstrated an outstanding track record of investment and innovation that has underpinned remarkable growth, and with it new trade and jobs".

"The lease process has delivered on many levels and we have ensured that employees, port users and the Government's interests are well protected. This is a fantastic outcome for the Territory," he said.

Before the deal's announcement the NT Government attempted to address environmental concerns about an expansion of operations in the area, which included Aboriginal cultural sites and World War II historic sites.

"We understand the need to protect our natural environment. Any lease of the port, and ongoing operation by a private investor, would need to comply with NT and Federal environment regulations," the Government said on a department website.

In a statement, the Government said it would continue to maintain safety standards at the port:

The Government has implemented safeguards to retain full oversight of safety regulation and operations, including the role of Regional Harbourmaster transferring to the Department of Transport. The Government retains powers in relation to the licensing of stevedores and the prevention of localised monopolies or vertically integrated activities at the port. The Territory has step-in rights to correct breaches of key operating standards. The planning and environmental regulations remain unchanged.

No jobs loss guarantee until 2018

Landbridge's Mike Hughes said the company planned on making a "considerable financial investment" in the port.

Sorry, this video has expired Overview of proposed development at Port of Darwin

"Landbridge intends to grow two-way trade between Australia and Asia, leveraging Landbridge's existing port and logistics businesses and firmly putting Darwin on the map for Chinese business," he said.

"We plan on making considerable financial investment in the Port of Darwin.

"In addition to committing an initial $35 million of new growth investment expenditure over the first five years, we anticipate in excess of $200 million of capital expenditure over the next 25 years. Given the scope of development opportunities in the Territory, we hope to invest a lot more."

Landbridge said it intends to "maintain the established workforce at the Port of Darwin" at least until 2018.

"There will be no forced redundancies during the term of the current enterprise agreement (which terminates in June 2018)," Mr Hughes said in a statement.

"Landbridge also intends to implement a stable and competitive pricing regime for port services with no more than CPI indexed pricing adjustments for the use of current port facilities.

Landbridge Group is owned by Chinese billionaire Ye Cheng.

Forbes lists 53-year-old Mr Cheng as chair of the privately-held Shandong Landbridge Group, which it said is "active in petrochemicals, logistics, real estate and international trade" as well as port operations.

Forbes lists Mr Cheng as having a 2015 net worth of $1.37 billion.

Deal a 'cash grab', Labor says

NT Oppostion Leader Michael Gunner described the deal as "nothing more than another one off cash grab by the CLP Government, just like the last budget and TIO".

"Labor would have done hard yards on Private Port infrastructure with joint agreements, just as we did with [the] Marine Supply Base," Mr Gunner tweeted soon after the announcement.

He said the CLP had no mandate to sell Private Port and that a decision "of this magnitude" should be determined by the people.

Mr Gunner said while Territory Labor "disagrees and fought against CLP's port sale, responsible government means we must honour the contract of the sale".

Union 'strongly condemns' deal

In a statement to the ABC, Thomas Mayor, the NT Maritime Union of Australia (MUA) branch secretary, slammed the deal with Landbridge.

"On behalf of the MUA, I strongly condemn the sale of the publicly-owned Port of Darwin to a private Chinese investment firm.

"From day one this deal has been shrouded in secrecy and Chief Minister Adam Giles has failed to engage in a meaningful way on a decision that will negatively impact every Territorian for years to come.

"Mr Mayor said the port was "a profitable piece of infrastructure that provided a revenue stream for much-needed health, education and other public services and this has been sold off for a short-term windfall.

"In the absence of good judgement on this deal, I am now demanding the Giles Government come to the table and discuss the future for the workers engaged at the port."

Mr Mayor said "no jobs should be lost as a result of this sale".

"The workers want assurances that their conditions are protected for the life of the lease and that jobs will not be contracted out.

"If these conditions will not be agreed to by October 19, we will use our full arsenal to fight Giles and his Federal Liberal Party crony Natasha Griggs."