Around a dozen nationalists raised Japanese flags on an island at the heart of a territorial row between the two countries, just days after Tokyo deported pro-Beijing protesters who had landed on the island.

The English-language China Daily newspaper said the unfurling of Japanese flags on the island was an "affront" to China's sovereignty.

"Japan is building another wall in its relations with China and the Japanese intruders and their government seem hell-bent on freezing Sino-Japanese ties," it said an editorial.

"It would be a mistake for Japan to see China's use of reason and restraint to deal with the Diaoyu Islands dispute as its weakness," the editorial said, using China's name for the island chain, which Japan calls Senkaku.

China's foreign ministry registered a "strong protest" with Japan on Sunday after the landing and urged Tokyo to put ties back on track.

The People's Daily newspaper, mouthpiece of China's ruling communist party, said Japan should recognise the consequences of its actions.

"Using the Diaoyu Islands issue to pick a quarrel and provoke an incident with China not only damages Sino-Japanese relations but also hurts the feelings of the Chinese people," it said in an editorial.

Thousands of Chinese citizens in more than 20 cities protested on Sunday, in what some analysts said was the biggest wave of anti-Japanese sentiment since 2005, when several cities also saw protests over several issues.

The People's Daily called for negotiations to resolve the issue, repeating a similar call by the Chinese government made on Friday.

But the Global Times newspaper, known for its nationalistic stance, warned China could reciprocate if Japan increased its defence of the islands.

"China will definitely take further steps regarding Diaoyu," it said. "The reluctance to resort to military means doesn't mean China is afraid of war."

Japan detained and then released 14 pro-China activists and journalists who sailed from Hong Kong to land on the islands last week.

"They showed up at Yaeyama Police Station at 11am... Interviews of them have started," an official at Okinawa police in Japan's southernmost prefecture told AFP by telephone.

The questioning was being done on a voluntary basis and the local police were trying to "get a handle on what happened", the official said.

The police were examining whether the landing was "appropriate under the law", he said while declining to give further details.

Japanese media said the ten could be charged with a minor offence for landing on the island without proper government permission.

Four members of a local assembly in Okinawa, who landed on the island in January and were questioned by the police, were not charged.

On Sunday members of the right-wing group Gambare Nippon (Hang In There Japan) swam ashore from a 20-boat flotilla carrying activists and lawmakers.

The landing came just days after Tokyo deported pro-Beijing protesters who had landed on the island, part of a chain administered by Japan but claimed by China, which said Sunday's action was illegal.

They had spent around five hours at the islands, known as Senkaku in Japan and Diaoyu in China.

Japanese coastguard ships had urged the activists not to land, with officers boarding some of the vessels to question people. No arrests were made.

Japan rejects China protests over island landing
Tokyo (AFP) Aug 20, 2012 - Tokyo on Monday rejected Chinese protests over the raising of a Japanese flag on a disputed island, but called for progress in "mutually beneficial" relations with Beijing.

Chief Cabinet Secretary Osamu Fujimura said Beijing and Taipei had both objected after 10 Japanese nationalists landed on an archipelago in the East China Sea on Sunday.

"We have explained our nation's basic position and told them that we cannot accept their claims," the government's top spokesman told a news conference in Tokyo.

"There is no doubt that the islands are our sovereign territory historically and under international law, and our nation effectively controls the islands," he added.

Fujimura said Japanese authorities were handling the case "in accordance with domestic law" as the nationalists broke regulations banning landing on the islands, known as Senkaku in Japan and Diaoyu in China.

Japan on Friday deported pro-Beijing activists who had landed on the islands, drawing flak at home from right-wingers, who insisted the 14 should have been punished for entering Japan illegally.

But Fujimura insisted that neither Tokyo nor Beijing has any interest in seeing overall relations affected by the dispute.

"The Japan-China relationship is one of the most important bilateral ties for Japan," he said.

"China's constructive role is necessary for the stability and prosperity of the Asia-Pacific region," he said. "We would like to continue to further progress mutually beneficial relations between Japan and China."

Fujimura also called on the Chinese government to ensure the safety of Japanese nationals in China as anti-Japan protests broke out there targeting Japanese businesses, restaurants and cars.

The Japanese foreign ministry has separately issued a travel advisory, telling Japanese nationals to be on alert while staying in the country.