Japan and South Korea said Thursday they have defied China's newly-declared air defence zone, showing a united front to Beijing after US B-52 bombers did the same.

Chinese authorities are coming under internal pressure to toughen their response to incursions into the air defence identification zone (ADIZ), which it declared unilaterally last weekend.

It 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.

The Chinese ADIZ requires aircraft to provide their flight plan, declare their nationality and maintain two-way radio communication -- or face "defensive emergency measures".

But Tokyo's well-equipped coastguard said it had flown unopposed in the zone without complying with Beijing's rules, and a report said the country's air force had done the same.

"We've not changed our normal operation of patrolling the area where China declared its defence zone without reporting flight plans," Yasutaka Nonaka, spokesman for Japan's coastguard told AFP. "We've not encountered Chinese jets."

The South Korean 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 had flown into the zone -- an unmistakable message from Washington before a visit to the region by Vice-President Joe Biden.

China's defence ministry issued a statement 11 hours after the US announcement saying the 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 the "psychological battles" by the US.

The government-run China Daily added that Washington's move risked increasing Tokyo's "dangerous belligerence" and putting China and the US "on a collision course. Which will prove much more hazardous than sending military aircraft to play chicken in the air".

China's Communist party gains support by tapping into deep-seated popular resentment of Japan for its brutal invasion of China in the 1930s.

Such passions are quickly aroused, and Chinese social media users called for Beijing to retaliate against Washington.

"The US's bomber wandered around the edge of our ADIZ, I figure we should respond in kind. One good turn deserves another, right?" wrote one commentator on Sina Weibo, a social media service similar to Twitter.

Senior administration officials in Washington said on Wednesday that Biden plans to raise Washington's concerns about the zone during his visit to Beijing next week.

The trip will allow him to "make the broader point that there's an emerging pattern of behaviour by China that is unsettling to China's own neighbours and raising questions about how China operates in international space", an official said.

China's relations with South Korea have recently improved but the zone covers a disputed South Korean-controlled rock -- known as Ieodo in Seoul and Suyan in Beijing -- 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 unilateral announcement of the ADIZ, 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, 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.

China for its part has accused the US and Japan -- which have both maintained ADIZs for years -- of double standards, and says the real provocateur is Tokyo.

The islands dispute lay dormant for decades but flared up in September 2012 when Tokyo purchased three of the uninhabited outcrops from private owners.

Beijing accused Tokyo of altering the status quo and has since sent surveillance ships and aircraft to the area as shows of force, prompting Japan to scramble fighter jets 386 times in the 12 months to September.

After an unidentified drone flew towards the islands, Tokyo threatened to shoot down such aircraft, which Beijing warned would amount to an "act of war".

The manoeuvres have raised fears of an accidental clash.