Japan tightened its cordon of boats yesterday around a set of remote islands also claimed by China, blocking any new visits by activists that would inflame the dispute, while Beijing demanded that Tokyo release seven Chinese who landed on the isles this week.
Japanese police late yesterday said they would hand the activists over to immigration authorities, Japanese media said.
Immigration officials were likely to deport the activists, government sources had said earlier.
Japan's detention on Wednesday of the activists was the first such arrests in the international dispute over the archipelago known as Diaoyu in China and Senkaku in Japan. The islands are also claimed by Taiwan.
The incident further aggravates relations between Tokyo and Beijing, already tense over Japanese leader Junichiro Koizumi's annual visits to a war shrine, which Asian nations say glorifies Japan's militaristic past.
In China, state-run newspapers earlier yesterday trumpeted demands that Japan release the activists. About 50 protesters congregated outside the Japanese Embassy in Beijing, holding up banners claiming the islands as Chinese territory.
Japanese Coast Guard spokesman Masayoshi Iramina said vessels guarding the uninhabited islands were on heightened alert, but refused to say how many more ships had been added to regular patrols.
Japanese authorities had questioned the seven Chinese activists arrested for their allegedly illegal visit to the isle of Uotsuri.
The China Federation for Defending the Diaoyu Islands, which sent the first batch of activists, said it planned another trip to the island on Sunday with more than 30 people.
Japan's National Public Safety Commission chief, Kiyoko Ono, said the Chinese activists violated immigration laws and stressed that authorities would prevent any others, including Japanese, from reaching the island.
On Thursday, police stopped a Japanese right-wing extremist group from leaving for the island from nearby Okinawa.
"Our government disapproves of landings by Japanese," Ono said. "It goes without saying that we will reject foreign visitors, too."
Japan took control of the islands, located between Taiwan and Japan, when it defeated China in the 1895 Sino-Japanese war. The US had jurisdiction over them after WWII until 1972, when they were handed back to Japan. China says its claim dates back centuries.
Tokyo and Beijing have issued competing claims of ownership over the island. On Thursday, Beijing called the arrests "a challenge to Chinese sovereignty." Tokyo said the activists trespassed on Japanese land despite warnings to stay away.
The Chinese activists left the southeastern province of Zhejiang on a trawler on Wednesday, and reached the disputed island aboard smaller boats. The activists said they wanted to draw attention to China's claim over the island chain.
China had demanded Thursday that Japan release the activists "without any conditions."
Meanwhile, protesters in Beijing and Hong Kong denounced the arrests and burned Japanese flags, prompting a strong protest from Foreign Minister Yoriko Kawaguchi, who is to visit China from April 3.
"The flag-burning was extremely regrettable," Kawaguchi said.
Koizumi has said he hoped the diplomatic repercussions of the incident would be limited.
Japanese media said the dispute was more than just symbolic.