China has sent warplanes into its newly declared maritime air defence zone, state media reports from Beijing say.
The flights came after South Korean and Japanese flights through the zone added to the international defiance of rules Beijing says it has imposed in the East China Sea.
China's air force spokesman Shen Jinke said several fighter jets and an early warning aircraft were sent on normal air patrols in the zone. He was quoted by the state news agency Xinhua.
Shen described the flights as "a defensive measure and in line with international common practices." He said China's air force would remain on high alert and will take measures to protect the country's airspace.
Without prior notice, Beijing began demanding on Saturday that passing aircraft identify themselves and accept Chinese instructions or face consequences in an East China Sea zone that overlaps a similar air defence identification zone overseen by Japan since 1969 and initially part of one set up by the US military.
That was tested just days later by US B-52 flights - with Washington saying it made no effort to comply with China's rules, and would not do so in the future.
South Korea's military said its planes flew through the zone this week without informing China and with no apparent interference.
Japan also said its planes have continuing to fly through it after the Chinese announcement, while the Philippines, locked in an increasingly bitter dispute with Beijing over South China Sea islands, said it also was rejecting China's declaration.