The Philippine military monitored a Chinese "carrier battle group" near the territorial waters of the country in Northern Luzon.

In an interview with reporters during the sideline of the the Maritime Security Symposium in Manila on Thursday, Rear Admiral Roy Vincent Trinidad, Philippine Navy spokesman for the West Philippine Sea, said People's Liberation Army Navy (PLAN) aircraft carrier CNS Shandong was last seen almost within the bounds of the Philippine exclusive economic zone (EEZ) on the western part of Cagayan province as of Wednesday night.

"This was one of the larger or unusual formations we have monitored considering that we had the aircraft carrier with six warships, destroyers and frigates escorting her and two support vessels," he said.

According to Trinidad, the carrier battle group includes a total of nine PLAN vessels including aircraft carrier "Shandong, six escorts or warships and two support vessels."

"Surveillance ship is usually characterized generally as a support vessel. So a support vessel could be a surveillance ship, it could be a research vessel, it could be a replenishment oiler. They are generally support vessels and warships or escorts," he added.

China's carrier battle group was first detected at 101.3 nautical miles northwest off Burgos, Ilocos Norte around 3 am of April 22 until it reached as close as about 2.23 nautical miles southwest of Babuyan Island at around 9:36 am of the same day.

"The closest to our islands in the north was roughly three nautical miles while this is quite close but these are allowed under UNCLOS under the right of innocent passage provided that it is continuous and expeditious," he said

"As of last night, they were almost within the outer boundaries of our EEZ. They were roughly 180 nautical miles east of Aparri, Cagayan," he added.

Trinidad confirmed that the Philippine military challenged the presence of the carrier battle group but they didn't get any reply.

"We always challenge foreign warships passing through our territorial waters to our EEZ. This time we didn't get any reply. While the normal procedure is for warships or foreign ships to reply, there are some instances that they don't reply. This is one particular instance that the Shandong carrier battle group did not give any reply. At the moment it was challenged," he said.

"We have encountered different warships and even merchant vessels in the past that do not respond. So it is not totally uncommon for warships or merchant vessels not to respond to any challenge," he added.

Trinidad noted that there is no need to file diplomatic protest against China on the monitored presence of the carrier battle group as it traverses the Philippine waters in continuous and expeditious way from west to eastern part of Northern Luzon. Robina Asido/DMS