Japan and South Korea said they have defied China's newly-declared air defence zone with military overflights, showing Beijing a united front after US B-52 bombers did the same.
The new defence zone, announced by China at the weekend, requires foreign aircraft to identify themselves and maintain open communication with Chinese authorities upon entry into the airspace.
We have been operating normal warning and patrol activities in the East China Sea including that area. We have no intention of changing this.
Japan, South Korea and the US disregarded these requirements and a Japanese official said the country's coast guard and air force will continue to ignore Beijing's regulations.
"We have been operating normal warning and patrol activities in the East China Sea including that area," Yoshihide Suga, Chief Cabinet Secretary, said on Thursday. "We have no intention of changing this."
South Korea's military said it was met with no resistance when its planes flew into the defence zone.
The zone 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 zone also includes a South Korea-controlled rock that has long created tension with China.
South Korea's vice defence minister, Baek Seung-Joo, said he was disappointed by China's decision to declare the air defence zone, which he said would only create further problems between the countries.
On Wednesday, two giant US Stratofortress bombers flew into the zone, an unmistakable message from Washington before a pre-planned visit to the region by US Vice President Joe Biden.
The visit will now include discussions over the zone, senior administration officials in Washington said.
The trip will allow Biden 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," one official said.
'Chicken in the air'
China's defence ministry issued a statement 11 hours after the US flights, saying its military had "monitored the entire process."
But Chinese authorities are under growing pressure from the ruling Communist Party to take action against countries that defy the zone.
The Global Times, a government-run Chinese Daily, published an editorial on Thursday that said Washington's breach risked worsening Japan's disobedience.
It could put China and the US on a collision course "which will prove much more hazardous than sending military aircraft to play chicken in the air," said the daily.
Qin Gang, China's foreign ministry spokesman, also advised both the US and Japan to "immediately correct their mistakes and stop their irresponsible accusations against China."
Terms of the zone stipulate that aircraft that fail to declare their nationality and maintain open communication will face "defensive emergency measures."
So far China has only issued verbal warnings.
Source: Al Jazeera and agencies