Beijing has accused Tokyo of interfering in disputes over the South China Sea after the Philippines said it would lease five planes from Japan to help patrol the contested waters.
On Thursday, Chinese Foreign Ministry spokesman Hong Lei said Beijing was “resolutely opposed” to challenges to its sovereignty and security and would “remain on high alert.”
China claims sovereignty over nearly all of the South China Sea, which is also claimed in part by Taiwan, Brunei, Vietnam, Malaysia, and the Philippines.
"We urge the Japanese side to mind its words and actions and refrain from undermining the peace and stability of the region," Lei said.
Last week, defense ministers from the Philippines and Japan signed a defense equipment and technology agreement, formalizing an arrangement already approved in principle in November 2015.
Philippine President Benigno Aquino confirmed that the Southeast Asian state would lease “from Japan five TC-90 training aircraft to assist our navy in patrolling” what the Philippines views as its territory.
Aquino did not say when the Japanese aircraft would arrive.
The Philippine military is allocating 83 billion pesos ($1.77 billion) until 2017 to upgrade and modernize its air force and navy.
The US and South Korea, both allies of the Philippines, have already offered help to bolster the country's air capabilities. Aquino announced the arrival this year of two refurbished C130 transport planes from the United States.
The Philippine military already plans to acquire a squadron of multi-role fighters, air-to-ground missile batteries, early warning aircraft and drones.
Relations between China and Japan have long been troubled by a territorial dispute as well as by what China regards as Japan’s failure to properly compensate its World War II-era atrocities.