Taiwan's defence ministry says it is asking Google to blur satellite images showing what experts describe as new military installations on Itu Aba, Taipei's sole holding in the disputed South China Sea.

The revelation of new military-related construction could raise tensions in the contested waterway, where China's building of airstrips and other facilities has worried other claimants and the United States.

The images seen on Google Earth show four three-pronged structures sitting in a semicircle just off the north-western shoreline of Itu Aba, across from an upgraded airstrip and recently constructed port that can dock 3,000-tonne frigates.

After local media published the images of Itu Aba, Taiwan Defence Ministry spokesman Chen Chung-chi said:

"Under the pre-condition of protecting military secrets and security, we have requested Google blur images of important military facilities."

The United States has urged against the militarisation of the South China Sea, following the rapid land reclamation by China on several disputed reefs through dredging, and building air fields and port facilities.

Taiwan's defence ministry and coast guard, which directly oversees Itu Aba, said details about the structures were confidential and have not commented on their nature.

Google, a unit of Alphabet Inc, said it was reviewing the request from Taiwan, but that to date such requests had not resulted in Google blurring imagery.

Satellite images used on Google Earth and Google Maps come from third-party providers, which Google purchases for use in its mapping system, according to the search giant.

"We take security concerns very seriously, and are always willing to discuss them with public agencies and officials," Google spokesman Taj Meadows said in an emailed response.

Defence experts in Taiwan said, based on the imagery of the structures and their semicircular layout, the structures were likely related to defence and could be part of an artillery foundation.

Dustin Wang, a scholar and a former government advisor who has regularly visited Itu Aba, said:

"I think definitely it will be for military purposes, but I cannot tell if it is for defending, attacking or monitoring."

Mr Wang said, given the structures' location, which faces the main seaborne traffic, they may relate to surveillance.

China, Taiwan, the Philippines, Vietnam, Malaysia and Brunei claim parts or all of the South China Sea, through which trillions of dollars in trade passes.

In July, an international court ruled against China in a case brought by the Philippines that rejected China's claim to a vast swathes of the disputed maritime area.

Both China and Taiwan, which China views as a renegade province, vehemently rejected the court ruling.

Reuters