Tokyo summoned Beijing's envoy on Thursday after Chinese government ships entered Japanese territorial waters near islands at the centre of a bitter row between the Asian giants.

The Chinese vessels entered the area early Wednesday and left around noon on Thursday, the Japanese coastguard said, the longest incursion since the dispute erupted again last year.

Tokyo issued a protest to acting ambassador Han Zhiqiang over the latest incident, a Japanese foreign ministry spokesman told AFP.

"The Chinese side argued its... position and said it could not accept Japan's protest," he said.

The incursion was the latest in a series by Chinese government ships in recent months around the Senkaku islands, a potential flashpoint that some observers say could even lead to armed conflict.

Beijing also claims the chain, which it calls the Diaoyus. The East China Sea archipelago is located in rich fishing grounds and is believed to harbour vast natural resources below its seabed.

Chinese foreign ministry spokesman Hong Lei confirmed coast guard vessels had patrolled waters around the islands and said the patrols were designed to exercise China's sovereignty, the official Xinhua news agency reported late Thursday.

"The Diaoyu island(s) and their affiliated islets are an integral part of Chinese territory and have been since ancient times," Hong was quoted as saying.

The Chinese ships left the area around midday, the Japanese coastguard said, adding that the longest previous stay by Chinese vessels was about 14 hours in February.

"The latest incident marks the longest stay" since last year, a coastguard official told AFP.

The long-running dispute flared again after Japan nationalised some of the disputed chain last September, setting off a diplomatic row and sparking riots across China.

A Chinese boycott of Japanese brands quickly followed, weighing on exports to the key market.

The territorial tensions and maritime skirmishes have all but frozen relations. A survey Thursday found that Chinese and Japanese people hold the least favourable views of each others' countries for almost a decade.

A total of 92.8 percent of Japanese have a bad or relatively bad impression of China, while 90.1 percent of Chinese hold similar feelings towards Japan, according to the poll by the state-run China Daily and Japanese think tank Genron NPO.

On Tuesday Beijing made strong criticism after Japan unveiled its biggest warship since World War II, a $1.2 billion helicopter carrier aimed at playing a major role in disaster and rescue missions, as well as defending sea lanes and Japanese territory.

"We express our concern at Japan's constant expansion of its military equipment. This trend is worthy of high vigilance by Japan's Asian neighbours and the international community," China's defence ministry said.

"Japan should learn from history, adhere to its policy of self-defence and abide by its promise of taking the road of peaceful development."

The comments came as Tokyo considers an overhaul of the pacifist constitution imposed on Japan by the United States after WWII. The prospect stirs strong emotions among Japan's neighbours.

Beijing and Seoul have long maintained that Tokyo has never come to terms with its militaristic past, including the brutal 1910-1945 occupation of the Korean peninsula.

Japan's well-funded and well-equipped military is referred to as the Self-Defense Forces, and is barred from taking aggressive action.

Any move to strengthen the military would require constitutional change, a move that Prime Minister Shinzo Abe's conservative administration has been eyeing since it swept December elections.