Taiwan's coast guard said on Friday that it had warned off and shadowed a Chinese research ship sailing in sensitive waters to the island's west, the third time the vessel has appeared since May in what Taipei sees as ongoing maritime provocation.
China views democratically governed Taiwan as its own territory and recognises no claims of sovereignty by the government in Taipei, including in the waters around the island.
Taiwan has complained of regular appearances by Chinese ships, including China's coast guard, in waters near Taiwan as part of "grey zone" harassment designed to pressure Taipei and give an impression of Chinese jurisdiction.
The coast guard said that the ship, the Tongji, which was commissioned only last year, appeared late Thursday 24.9 nautical miles northwest of the Penghu islands, which lie in the strait and are home to major Taiwanese military bases.
The ship was not observed deploying or towing any instruments and the coast guard said it sent one of its patrol boats to sail alongside the Tongji and broadcast "strong" warnings for it to leave.
As of Friday morning, the ship was 28 nautical miles west-southwest of Taiwan's Liuqiu island, a popular tourist destination at the bottom part of the strait, continuing to sail southeast, the coast guard said in a statement.
China's Taiwan Affairs Office did not immediately respond to a request for comment.
Taiwan's coast guard said it would proactively deploy its ships to respond to Chinese vessels, "firmly defending national sovereignty and ensuring the safety of our nation's waters".
China's military also operates around Taiwan on an almost daily basis.
Taiwan first spotted the Tongji in waters near the island in May, saying that at least on one occasion it was observed lowering ropes into the water, suspected to be the deployment of scientific instruments for "illegal" survey operations.
Chinese state media says the Tongji has all-weather operational capability and can carry remotely operated vehicles, laboratories and unmanned systems.
