China fired flares at a Philippine aircraft as it flew patrols over the South China Sea this month, according to the National Task Force for the West Philippine Sea.
Beijing claims most of the strategic waterway and has been involved in tense maritime confrontations with Manila in recent months, sparking fears of armed conflict that could draw in the United States, a Filipino military ally.
A Chinese fighter jet "engaged in irresponsible and dangerous maneuvers" on August 19 as the Bureau of Fisheries and Aquatic Resources (BFAR) plane made a "maritime domain awareness flight" near Scarborough Shoal, the task force said.
The unprovoked Chinese "harassment" included "deploying flares multiple times at a dangerously close distance of approximately 15 meters from the BFAR Grand Caravan aircraft", the task force added in a statement.
Flares were also launched near the same plane from the China-held Zamora Reef (also called Subi Reef internationally) on 22 August as the patrol craft was "monitoring and intercepting poachers encroaching upon the Philippines' Exclusive Economic Zone and the territorial seas" of the Philippines, it added.
Flares are usually employed by military aircraft as decoys to protect them from missiles, but also for illumination.
China's foreign ministry said on Friday that two Philippine military aircraft flew into its airspace over Zamora Reef, which Manila also claims, on 22 August.
The Chinese side undertook "necessary countermeasures in accordance with the law, in order to protect its own sovereignty and security", it said in a statement.
The Philippine government said the BFAR plane was a civilian Cessna aircraft.
The Chinese statement did not mention any 19 August incident over Panatag or Scarborough Shoal, which China seized from the Philippines at the end of a 2012 standoff.
The Panatag Shoal incident occurred hours after Philippine and Chinese coast guard vessels collided near Escoda Shoal, with the Filipino side reporting structural damage on both of its patrol ships.
The shoal is located 140 kilometers (86 miles) west of the Philippine island of Palawan and about 1,200 kilometers from Hainan island, the nearest Chinese landmass.
The Philippines has also accused a Chinese air force plane of making a "dangerous maneuver" and dropping flares in the path of a Filipino air force plane that was patrolling over Panatag on 10 August.
In June, the Philippine military said one of its sailors lost a thumb in a confrontation off Ayungin Shoal when the Chinese coast guard, wielding sticks, knives and an axe, also confiscated or destroyed Philippine equipment including guns.
Beijing has blamed the escalation on Manila and maintains its actions to protect its claims are legal and proportional.
It has continued to press its claims to almost the entire West Philippine Sea despite an international tribunal ruling that its assertion has no legal basis.
Manila on Saturday urged Beijing to "immediately cease all provocative and dangerous actions that threaten the safety of Philippine vessels and aircraft engaged in legitimate and regular activities within Philippine territory and Exclusive Economic Zone", as well as freedom of navigation and overflights.
"Such actions undermine regional peace and security, and further erode the image of the PRC (People's Republic of China) with the international community," the task force statement said.