Japan and South Korea have both flown planes unannounced through China's newly-declared air defence zone, officials from both nations say.
Japanese aircraft had conducted routine "surveillance activity" over the East China Sea zone, the top government spokesman said.
South Korea had also conducted a flight, its defence ministry said.
China says planes transiting the zone, which covers areas claimed by Tokyo, Seoul and Taipei, must file plans.
The zone includes islands known as Senkaku in Japan and Diaoyu in China which are claimed by Japan, China and Taiwan.
Japan controls the islands, which have been the focus of a bitter and long-running dispute between Japan and China.
The zone also covers a submerged rock that South Korea says forms part of its territory.
China, which established the air defence identification zone (ADIZ) on Saturday, says aircraft must report a flight plan, communicate and identify themselves. Those who do not could face "defensive emergency measures".
The move has been condemned by the US and Japan.
America, which called the move a ""destabilising attempt to alter the status quo in the region", flew two unarmed B-52 bombers through the zone unannounced on Tuesday.
