Hu demanded that the Japanese side immediately release the ship and crew members on board and guarantee the safety of the persons and the ship.

Chinese Vice Foreign Minister Song Tao on Tuesday summoned the Japanese ambassador and lodged solemn representations on Japan's interception of the Chinese fishing boat.

Foreign Ministry Spokeswoman Jiang Yu had expressed grave concern over the incident earlier Tuesday.

"The Diaoyu islands and its adjacent islets have been Chinese territory since ancient times," Jiang said at a regular press conference when asked to comment on the issue.

"We demand Japanese patrol boats refrain from so-called law enforcement activities in waters off the Diaoyu islands and actions that would threaten the safety of Chinese fishing boats and their crew," Jiang said.

"We will closely follow the situation and reserve our right to take further actions," Jiang said.

In Tokyo, the Chinese embassy to Japan made solemn representations with the Japanese Foreign Ministry over the arrest, demanding the immediate release of the captain and the boat to avoid an escalation of the incident, the embassy said.

Japanese Chief Cabinet Secretary Yoshito Sengoku said Wednesday Japan and China are trying to handle the situation calmly, and the incident will not affect Japan-China relations.

"We will handle the matter firmly in accordance with law," he told reporters, according to Kyodo News agency. "It is necessary for Tokyo not to heat up in dealing with the incident."

The islands appeared on China's map since the Ming Dynasty (1368-1644).

There are records about the islands in a book published during the rule of Yong Le (1403-1424) in the Ming Dynasty, more than 400 years before Japan claimed discovery of the Diaoyu islands in 1884.

Japan never questioned China's sovereignty over the islands before the Sino-Japanese war of 1894-1895.

Geologically, the islands are attached to Taiwan. The waters around the islands are 100 to 150 meters deep, and there is a 2,000-meter-deep oceanic trench between the islands and Japan's Okinawa islands.

Fishermen from China's Taiwan and Fujian and other provinces have conducted activities such as fishing and collecting herbs in this area since ancient times.

In June 2008, a Taiwanese fishing boat and a Japanese patrol boat collided about 9 km south of the Diaoyu Islands. The Taiwanese ship sank but all crew members were rescued.