China's Landbridge group was granted a 99-year lease on the port in 2015, a widely criticised decision that led to stricter scrutiny of infrastructure sales.

Prime Minister Anthony Albanese promised last year to buy back control, criticising the lease as short-sighted for both economic and national security reasons.

If Landbridge is obliged to give up the lease, "then we have an obligation to take measures to protect the Chinese company's interest -- that is our position," ambassador Xiao Qian told Australian media on Wednesday.

"We will see when it's time for us to say something, do something, to reflect the Chinese government's position and protect our Chinese companies' legitimate interests," he said.

The ambassador warned that retaking control of the port could affect Chinese companies' investment, cooperation and trade with the Darwin region.

"That is not in the interest of Australia either."

Australia's prime minister said his government had already made it clear that it disagreed with the port's sale to "non-Australian interests".

"We are committed to making sure that that port goes back into Australian hands because that is in our national interest," he told reporters Wednesday during a visit to East Timor.

Darwin lies closest to Australia's Asian neighbours and has been used as a base for US Marines.

At the time of the agreement, then-US president Barack Obama reportedly complained that Washington had not been told of Australia's plan to do business with Landbridge.