The Chinese planes had conducted normal air patrols on Thursday as "a defensive measure and in line with international common practices," said Shen Jinke, spokesman for the People's Liberation Army (PLA) Air Force, according to state news agency Xinhua.
Shen said China's air force would remain on high alert and take measures to protect the security of the country's airspace, Xinhua reported.
Japan and South Korea said Thursday they had defied the air defence identification zone (ADIZ) declared by Beijing last weekend, showing a united front after US B-52 bombers did the same.
Chinese authorities are coming under domestic pressure to toughen their response to incursions into the zone that includes disputed islands claimed by China, which knows them as the Diaoyus, but controlled by Japan, which calls them the Senkakus.
The move triggered US and Japanese accusations of provocation as global concerns grew.
China's ADIZ requires aircraft to provide their flight plan, declare their nationality and maintain two-way radio communication - or face "defensive emergency measures".
But Tokyo said its coastguard and air force had flown unopposed in the zone without complying with Beijing's rules.
"We have been operating normal warning and patrol activities in the East China Sea including that area," said Chief Cabinet Secretary Yoshihide Suga. "We have no intention of changing this."
South Korea's military said it encountered no resistance when one of its planes entered the area -- which also overlaps Seoul's ADIZ - unannounced on Tuesday.
A day earlier two giant US Stratofortress bombers flew into the zone, an unmistakable message from Washington before a pre-planned visit to the region by Vice President Joe Biden.
China's defence ministry issued a statement 11 hours after the US announcement saying its military "monitored the entire process" of the B-52 flights, without expressing regret or anger or threatening direct action.
The Global Times, which is close to China's ruling Communist Party and often takes a nationalist tone, criticised the reaction as "too slow" in an editorial Thursday.
"We failed in offering a timely and ideal response," it said, adding that Chinese officials needed to react to "psychological battles" by the US.
Asked about the South Korean flight, China's foreign ministry spokesman Qin Gang said: "China identifies any aircraft within the ADIZ and must have noted the relevant situation you have mentioned."
He reiterated criticism of US and Japanese responses to the zone, urging both countries to "immediately correct their mistakes and stop their irresponsible accusations against China".
The Communist Party seeks to drum up popular support by tapping into deep-seated resentment of Japan for its brutal invasion of China in the 1930s.
Nationalist passions easily aroused
Such nationalist passions are easily aroused, and Chinese social media users called for Beijing to retaliate against Washington.
Senior administration officials in Washington said Wednesday that Biden will raise Washington's concerns about the zone while in Beijing.
China's relations with South Korea have recently improved but the zone covers a disputed South Korean-controlled rock that has long been a source of tensions between them.
South Korea's Vice Defence Minister Baek Seung-Joo expressed "strong regret" at China's ADIZ announcement, which he said was "heightening military tension in the region."
Australia on Thursday refused to back down from criticism of the air zone after summoning China's ambassador earlier this week and prompting an angry response from Beijing.
The Philippines voiced concern that China may extend control of air space over disputed areas of the South China Sea, where the two nations have a separate territorial dispute.
Japanese passenger airlines said after government pressure they will not obey Beijing's rules, while the State Department has taken an ambiguous position, saying it was advising US carriers "to take all steps they consider necessary to operate safely in the... region".
Thai Airways said Thursday it will comply with Beijing's directive.
China for its part has accused the US and Japan - which both have ADIZs - of double standards, saying the real provocateur is Tokyo.
Defence ministry spokesman Yang Yujun said in a statement Thursday that Japan established its ADIZ in 1969, so Tokyo had "no right to make irresponsible remarks" about China's.
"If there are to be demands for a withdrawal, then we invite the Japanese side to first withdraw its air defence identification zone, and China may reconsider after 44 years," he said.
The islands dispute lay dormant for decades but flared in September 2012 when Tokyo purchased three of the uninhabited outcrops from private owners.
Beijing accused Tokyo of changing the status quo and has since sent surveillance ships and aircraft to the area, prompting Japan to scramble fighter jets 386 times in the 12 months to September.
The manoeuvres have raised fears of an accidental clash.