Brushing aside India's concern, China on Monday defended its submarines making port calls in Colombo, saying there is "nothing unusual" as it is an international common practice for warships to stop for refuelling at ports abroad.

"It is nothing unusual for the naval vessel to dock at Colombo port," official media quoted the Chinese Defence Ministry as saying.

"It is an international common practice for navy submarines to stop for refuelling and crew refreshment at an overseas port," an official from the Defence Ministry has been quoted as saying by state-run Xinhua news agency.

Nuclear submarine Changzheng-2 and warship Chang Xing Dao docked at the Colombo port on Friday, seven weeks after another Chinese submarine, a long-range deployment patrol, had called at the same port ahead of Chinese President Xi Jinping's visit to Maldives, Sri Lanka and India.

The official said the Chinese submarine docked during its escort missions in the Gulf of Aden and waters off Somalia. China has been deploying its warships in the Gulf of Aden operations to fight piracy.

Observers say that this is perhaps the first time that China began to deploy submarines, which would be frequenting the Indian Ocean.

China has been stating that it has no plans to build overseas military bases but at the same time its naval fleet have been securing refuelling and recreational facilities in places like Indian Ocean island of Seychelles and now Colombo port which has been partly financed by the Chinese government.

The Xinhua report said Sri Lanka allowed a Chinese submarine to dock at its Colombo harbour, despite concerns raised by India about China's warming relations with the island nation.

The report quoted Sri Lankan navy spokesman Kosala Warnakulasuriya as saying that there is nothing unusual in docking of the Chinese submarine.

"Since 2010, 230 warships have called at Colombo port from various countries on goodwill visits and for refuelling and crew refreshment," Warnakulasuriya has said.

Indian strategic analysts have voiced their concern over the frequent docking of Chinese naval ships in Sri Lanka.

(with inputs from Xinhua and PTI)