Thousands of Japanese demonstrated in front of the Chinese embassy in Tokyo on Saturday, stoking renewed diplomatic tensions between China and Japan, whose bilateral ties have plunged to their lowest level in years because Japan detained the captain of a Chinese fishing trawler near the Diaoyu Islands in the East China Sea.

Japanese fishermen also held a demonstration in Ginowan, Okinawa Prefecture, to protest the "illegal fishing by foreign nationals in Japanese waters," the Kyodo News Agency reported.

In China, demonstrations were held in at least three Chinese provincial capitals, including Chengdu of Sichuan Province, Xi'an of Shaanxi Province, and Zhengzhou of Henan Province on the same day.

More than 2,000 college students took to the streets in Chengdu, unfurling banners and shouting, "Defend the Diaoyu Islands" and "Fight Japan," the Xinhua News Agency reported.

Protestors in Mianyang, Sichuan Province, stoned a Japanese restaurant and smashed windows of Japanese cars, and they clashed with police as security forces tried to maintain order, Radio Television Hong Kong reported.

Chinese Foreign Ministry spokesman Ma Zhaoxu said Saturday that "China urges Japan to earnestly fulfill its obligations and take effective measures to ensure the security of China's embassy, consulates, institutions and personnel in Japan."

The latest Chinese protests came in the wake of a fishing row between China and Japan over the detention of Chinese fishing boat captain Zhan Qixiong after his trawler collided with two Japanese Coast Guard patrol boats near the island chain in the East China Sea.

The captain was released after Beijing strongly protested and suspended high-level dialogues. A thaw in relations had started to emerge, as Premier Wen Jiabao and his Japanese counterpart, Naoto Kan, met earlier this month on the sidelines of the Asia-Europe Meeting in Brussels and pledged to mend ties. China has also released four Japanese nationals detained since September 20 for illegally entering a Chinese military zone in Hebei Province.

Liu Jiangyong, vice director of the Institute of International Studies at Tsinghua University, said "right-wing protesters in Tokyo were both against Chinese and Japanese governments. They were happy with the occurrence of the incident and took advantage of it to show their existence and flex their muscles."

Huang Dahui, a professor of Japanese politics at Renmin University of China, told the Global Times that "despite the close economic ties, the two countries lack political mutual trust, and good feelings among the general public of the two countries remain low."

Due to China's rapid economic growth and Japan's long-term economic downturn, a sense of crisis has brewed in Japan, and the anti-China sentiment among some Japanese has gained strength, he said.

"Under such circumstances, both China and Japan should avoid using nationalism to irritate each other. Otherwise, it will do nothing in improving the ties between the two countries," he added.