"We demand the Japanese side immediately release the Chinese captain unconditionally," said Foreign Ministry spokesman Ma Zhaoxu.

"China will take strong counter measures if the Japanese side clings obstinately to its own course and double its mistakes, and Japan shall bear all the consequences," Ma said in a press statement.

China has already suspended bilateral exchanges at and above the provincial or ministerial levels, halted contact with Japan on the issues of increasing civil flights and expanding aviation rights between the two countries, and the number of Chinese tourists to Japan has already plunged, according to the ministry.

Wang Hanling, a maritime law expert with the Chinese Academy of Social Sciences, told Xinhua, "Japan's forceful so-called law enforcement in the waters off the Diaoyu Islands were in defiance of the principles of international law as well as Chinese law, which showed that Japan allowed no delay in asserting so-called 'sovereignty' in the area."

"It also showed that Japanese politicians were short-sighted in considering Sino-Japanese relations," Wang added.

Zhou Jincheng, a student from China Youth University for Political Sciences, said that Japan should not cling obstinately to its own course, or it would only arouse more anger from the Chinese people.

At Capitan Zhan's coastal hometown of Xiaozha in southeast China's Fujian Province, his family and fellow fishermen are expecting his release.

Recalling his six days and five nights under Japanese detention, Kang Chunming, a member of Zhan's crew, told Xinhua he was "very worried about the captain's safety and well-being."

Kang said after Japanese authorities seized their boat, while living on the boat they had to sleep sitting up and many of them had become ill because of unclean drinking water.

Besides, the Japanese took them off the boat for interrogations on a daily basis and, on some occasions, only sent them back in the small hours.

Since Zhan was seized, a lot has changed in his family.