Chinese Defense Ministry said it is nothing unusual for its naval vessel to dock at Colombo port despite concerns raised by India.

Sri Lanka allowed a Chinese submarine to dock at its Colombo harbor in Colombo on Sunday, despite concerns raised by India about China's warming relations with the Indian Ocean island nation. Another Chinese submarine had called at the same port ahead of Chinese President Xi Jinping's visit to South Asia seven weeks ago.

"This is nothing unusual. Since 2010, 230 warships have called at Colombo port from various countries on goodwill visits and for refueling and crew refreshment," said Sri Lankan navy spokesman Kosala Warnakulasuriya.

"It is an international common practice for navy submarine to stop for refueling and crew refreshment at an oversea port," according to an official from China's Defense Ministry.

The official said the Chinese submarine docks during its escort missions in the Gulf of Aden and waters off Somalia.

However, India has already raised concerns over the frequency of Chinese visits to Sri Lanka, Indian officials said.