Ministry spokesman Kapila Fonseka said Chinese research ship Shi Yan 6, which has been in Colombo since Wednesday, would be allowed to carry out work for two days starting Monday.

Earlier, Sri Lanka allowed the vessel to enter the main port of Colombo only for "replenishments" over concerns raised by neighbouring India that the craft could be used to spy against them.

New Delhi is suspicious of China's increasing presence in the Indian Ocean and its influence in Sri Lanka, which is strategically placed halfway along key east-west international shipping routes.

A spacecraft-tracking Chinese vessel last year raised security concerns from India, and Sri Lanka prohibited it from undertaking any research activities while in its waters.

Fonseka said local scientists will be onboard Shi Yan 6 during two days of research activities along the western seaboard of the island.

"Apart from our scientists and researchers, the Sri Lanka navy too will be monitoring this vessel," Fonseka told AFP.

The 90-metre (300-foot) vessel is anchored at the Colombo harbour where a Chinese state-run company operates a deep sea terminal.

A pair of Chinese submarines docked there in 2014, raising protests from India.

There was no immediate comment from either the Chinese or Indian diplomatic missions in Sri Lanka after Colombo granted limited approvals to Shi Yan 6.

Chinese state broadcaster CGTN calls the Shi Yan 6 a "scientific research vessel" with a crew of 60 to conduct oceanography, geology and marine ecology tests.

Another Chinese research vessel, Yuan Wang 5, which specialises in spacecraft tracking and which New Delhi described as a spy ship, visited Sri Lanka last year.

It docked in Hambantota, a port in Sri Lanka's south under a 99-year lease to the Chinese company that built it after Colombo was unable to service a $1.4 billion loan taken for the project.

Sri Lanka defaulted on its $46 billion external debt last year in an unprecedented economic crisis partly blamed on Chinese loans used to build white-elephant infrastructure projects between 2005 and 2015.

China owns 52 percent of Sri Lanka's bilateral debt, and Beijing's approval is crucial for any efforts by Colombo to restructure its outstanding loans.