(BSS/AFP) - China will act to defend its companies` interests if Australia forcibly buys back control of the strategic northern port of Darwin, Beijing`s ambassador has warned.

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.