Japan accused China of flying fighter jets "dangerously" close to two of its military planes over the East China Sea Wednesday, as bilateral tensions simmer over the countries' territorial dispute.

Two Chinese SU-27 jets flew as close as 30 metres (100 feet) away from the Japanese defence aircraft at about 11am local time (0200 GMT), the defence ministry in Tokyo said.

Defence Minister Itsunori Onodera told reporters his ministry had lodged a diplomatic complaint with China over the incident.

It was the second time in less than three weeks that Tokyo accused Beijing of "dangerous" flights by Chinese fighter jets against Japanese military planes.

The alleged incident occurred over the open seas near the disputed waters where China's stated air defence identification zone overlaps with that of Japan.

The area is about 200-300 kilometres (125-190 miles) north of the Japanese-controlled Senkaku islands, which China also claims and calls the Diaoyus.

Defence Minister Onodera called the Chinese aircraft's manoeuvres "extremely dangerous flights that could have led to an accident."

"We cannot allow this to happen," he said, urging Beijing to preventing a recurrence by by establishing a hotline between their defence officials.

In an apparent tit-for-tat move, the Chinese defence ministry said on May 29 that two Japanese fighter planes came within 10 metres of a Chinese transport aircraft over the East China Sea in late November last year.

The territorial dispute flared in September 2012 when Tokyo nationalised some of the islands.

Chinese state-owned ships and aircraft, including coastguard vessels, have since approached the island group, sometimes venturing into its territorial waters and airspace, chased by Japanese coastguard patrols and prompting Tokyo to scramble fighter jets.

Fears of a military clash in the area have been heightened after China unilaterally declared last November the establishment of its air defence identification zone above the East China Sea, which overlaps a similar Japanese zone.