Prime Minister Yoshihiko Noda has called on China to ensure the safety of Japanese people and businesses amid a growing territorial row that has seen the spread of anti-Japan demonstrations.
His comments came as thousands of protestors gathered outside Japan's embassy in Beijing, a day after angry demonstrators tried to storm the building.
The rumbling territorial dispute reached a new level during the week when Japan announced that it had bought islands in the East China Sea which it administers and calls Senkaku, but which China claims and calls Diaoyu.
Anti-Japan demonstrations spread to 50 Chinese cities Saturday, Japanese reports said, with attacks on Japanese businesses, cars and restaurants.
"This situation is a great disappointment and so we are protesting (to China)," Noda told Fuji Television.
"We want (China) to oversee the situation so that at least Japanese citizens and businesses in China will not be in danger."
Noda stressed the importance for both countries to "behave with restraint".
"We are the number two and number three economies in the world, and China's development is in Japan's interest," he said.
"I believe we can overcome the problem if we keep in mind the broader viewpoint (of the bilateral ties)."
In Qingdao in northeastern China, 10 factories connected to Japanese businesses including Panasonic were targeted by protesters Saturday, the Yomiuri Shimbun reported, citing the Japanese embassy in China as a source.
There were arson attacks and production lines were destroyed, the newspaper said, and a supermarket outlet run by Japan's Aeon was looted.
Japanese media slammed the attacks as "beyond the pale".
"The Chinese government should stop provocative actions and call for restraints to its own people," the influential Asahi Shimbun said.
Often testy Japan-China ties took a turn for the worse in August when pro-Beijing activists landed on one of the disputed islands.
They were arrested by Japanese authorities and deported. Days later about a dozen Japanese nationalists raised their country's flag on the same island, Uotsurijima, prompting protests in cities across China.
Six Chinese ships sailed into waters around the archipelago Friday, with Beijing saying they were there for "law enforcement", leading Tokyo to summon the Chinese ambassador to protest what it insisted was a territorial incursion.
