A Chinese survey ship has been operating in sensitive waters off southwestern Taiwan, and Taiwan's coast guard is treating it as a possible military scouting mission.

• The Chinese research vessel Tongji was tracked west of Liuqiu island, a spot seen as prime submarine ambush ground near the navy's Zuoying base.
• Taiwan sent a patrol ship to shadow it, broadcast warnings, and steer it away from Taiwanese waters.
• The ship stayed just outside Taiwan's restricted zone and kept moving southeast, so there was no legal basis to board or stop it.
• Officials say the vessel was not towing or dropping any equipment, but its route through militarily valuable water raised alarm.

Outlook: Taiwan says it will keep tracking Chinese ships around the island with joint surveillance and pre-position patrol boats, so more of these close encounters are likely.