Japan was Thursday considering whether to prosecute or deport 14 people it arrested after pro-China activists landed on a disputed island, as Beijing angrily demanded their immediate release.

Five men, who became the first non-Japanese to set foot on the island for eight years, were in the Okinawan capital Naha where they were to be quizzed, police said.

"They were already taken to Naha city, and questioning will start today at separate police stations," a local police officer told agencies.

Journalists from Hong Kong-based Phoenix TV were among a further nine who were arrested at sea as the activists' boat prepared to move away from the island.

"The nine arrested yesterday are to arrive at the port of Naha in the evening," a spokesman at the local coast guard said.

The Okinawan prefectural police are expected to either turn the detainees over to immigration authorities for deportation or send the case to prosecutors for further investigation.

Up to 60 people protested at the Japanese consulate in Hong Kong on Thursday, demanding Japan release the activists and give up its claim to the island chain.

About a dozen members of the pro-Beijing Hong Kong Federation of Trade Unions waved Chinese flags and chanted slogans such as 'Down with Japanese militarism' and 'Get out of our Diaoyu Islands', the Chinese name for what Japan calls Senkaku.

Protest group leader Aron Kwok said the arrests had been unlawful and the 14 should be freed immediately.

"The Diaoyu Islands are part of Chinese territory, we do not tolerate any acts to challenge Chinese sovereignty. We strongly condemn Japan's action and we demand an apology."

An editorial in the People's Daily, the Chinese Communist Party mouthpiece, upbraided Japan and called on Tokyo to reflect on its actions 'from a deep level'.

"Disregarding history and refusing to engage in soul-searching is outrageous and unreasonable, and shows an unwillingness to see other opinions," it said.

"A country... that persists in... political wrongdoings and that cannot stand face-to-face with the international community cannot become a respected country no matter how much its economy grows."

The case is a delicate one for Japan, which has to balance popular annoyance at the landing with vehement demands from China for the immediate release of the group.

The consensus in local media on Thursday was that the authorities would deport the 14 within a few days, to avoid a repeat of the diplomatic bloody nose Japan received after holding a Chinese trawlerman for two weeks in 2010.

On that occasion, Tokyo was widely criticised as having caved in to Chinese pressure and being forced into releasing the man after Beijing halted high level contacts and stymied trade.

The group of activists had sailed from Hong Kong on Sunday to the archipelago, where pictures show they raised Chinese and Taiwanese flags.

Under Japanese law, a foreigner who does not have permission to be in Japan can be turned over to immigration authorities for immediate deportation when the individual is not facing other criminal charges.

In 2004, when a group of Chinese activists landed on a disputed island, then prime minister Junichiro Koizumi ordered their deportation after two days.

Tetsuro Kato, professor emeritus of politics at Tokyo's Hitotsubashi University, said: "Japan needs to handle the latest incident calmly by following the precedent of 2004, and it needs to review thoroughly how to rebuild its diplomacy."

The renewed dispute over the islands comes as Japan's relations with South Korea have become increasingly frayed after President Lee Myung-Bak visited islets controlled by Seoul but claimed by Tokyo.

Nearly 200 people held a rally in front of the South Korean embassy in central Tokyo, protesting against the visit and calling on Lee to apologise to the Japanese emperor.