The Philippine Coast Guard (PCG) challenged a Chinese research vessel by radio on Saturday, after it was tracked about 37 nautical miles off the coast of Sta. Ana. Cagayan.

In a statement on Sunday, the PCG ordered a plane to head towards the area where research ship Xiang Yang Hong 05. The plane tracked the ship at 14.92 nautical miles from Babuyan Island.

''The vessel was challenged but did not respond,'' it added. The ship left Guangdong province on June 6 and entered the Philippines' exclusive economic zone on June 9 only to re-enter last July 31. DMS