China says it scrambled fighter jets to monitor US and Japanese planes as they flew in its newly declared air defence zone in the East China Sea on Friday.
The zone covers territory claimed by China, Japan, Taiwan and South Korea.
China said last week that all aircraft crossing through the zone must file flight plans and identify themselves or face "defensive emergency measures".
The US, Japan and South Korea say they have since defied the ruling and flown military aircraft in the area.
The air defence identification zone (ADIZ) covers a vast area of the East China Sea, including a group of islands claimed by Japan, China and Taiwan.
South Korea claims a submerged rock, known as Ieodo, also within the zone.
The establishment of the ADIZ has caused widespread anger, with the US state department calling it "an attempt to unilaterally change the status quo in the East China Sea" which will "raise regional tensions and increase the risk of miscalculation, confrontation and accidents".
'Firm but calm'
On Thursday, China had announced it was deploying warplanes in the area for surveillance and defence.
Then on Friday, Air Force spokesman Col Shen Jinke said warplanes had been scrambled that morning to monitor two US surveillance aircraft and 10 Japanese planes - including early warning aircraft, surveillance aircraft and fighter jets - crossing through the ADIZ.
Col Shen said the jets had tracked the flights and identified the planes, state media reports.
Japanese officials gave no details of the flights, but said they were continuing to conduct routine operations in the region and had encountered no "abnormal instances so far".
Earlier, China's Foreign Ministry spokesman Qin Gang said China had a right to patrol the region and that the ADIZ was not aimed at any specific country.
"If some worry has emerged about the situation, it's agitated by some individual countries," he told a regular briefing.
If disputes existed, China wanted to solve them through "peaceful means via friendly negotiation," he said.
Japanese Prime Minister Shinzo Abe said on Friday that Japan would respond "firmly but in a calm manner" to China's move, the Kyodo news agency reports.
Foreign Minister Fumio Kushida said the issue would be discussed with US Vice-President Joe Biden, who is due to begin a three-day visit to Japan on Monday.
The disputed group of uninhabited islands in the zone are known as Senkaku in Japan and Diaoyu in Chinese.
They are controlled by Japan, but have been the subject of rising tensions in recent years because of their proximity to important shipping lanes, fishing grounds and potential fossil fuel reserves.
South Korea has complained to China that the ADIZ also overlaps its own similar defence zone, and encompasses the Ieodo rock.
A number of regional commercial airlines - including Singapore Airlines, Qantas and Korean Air - have said they will comply with China's new requirements.