Colombo's announcement will likely raise fresh concerns in New Delhi over China's military potentially getting a foothold in the Indian Ocean through the deep-sea port of Hambantota, which straddles a major east-west shipping route.

"The Sri Lanka navy is moving its Southern Command to Hambantota," Ranil Wickremesinghe's office said.

But it added: "There is no need to be frightened as security of the port will be under the control of the Sri Lanka Navy.

"Sri Lanka has also informed the Chinese that Hambantota cannot be used (by China) for military purposes," it said.

Sri Lanka owes China billions of dollars that former president Mahinda Rajapakse's government borrowed for major infrastructure projects, including the Hambantota port located on the island's southern tip.

But unable to pay back the debts, Sri Lanka agreed last year to give China a 70-percent stake in the port on a 99-year lease.

This stoked concerns in India and the US about China's Belt and Road initiative that has seen Beijing loan countries across Asia and beyond huge amounts of money, ostensibly to develop their infrastructure to ease trade.

The new government of President Maithripala Sirisena turned down a Chinese request in May last year for a submarine call at Colombo shortly after Indian Prime Minister Narendra Modi visited the island.

Two Chinese submarines had called at Colombo in 2014 during the final year of Rajapakse's tenure.

Sirisena came to power in January 2015 promising to loosen ties with China.