China must take steps to prevent violence against Japanese citizens, Japanese Prime Minster Yoshihiko Noda has said.
Anti-Japanese protests spread to cities across China on Saturday in an escalating row over disputed islands in the East China Sea.
On Sunday, hundreds of protesters faced off against riot police at the Japanese embassy in Beijing.
Japanese businesses have also been targeted by protesters.
"We want [China] to oversee the situation so that at least Japanese citizens and businesses in China will not be in danger," Mr Noda told Japanese TV, according to the AFP news agency.
"We will continue to take a resolute attitude. But we will also remain calm. Japan will ask the Chinese side to do the same," Kyodo news agency reported him as saying.
Protests were reported in dozens of Chinese cities on Sunday. The previous day's disturbances had seen Japanese businesses and even Japanese-made cars attacked.
One eyewitness in the city of Xi'an described to the BBC how his camera was snatched from him and damaged because it was a Japanese brand.Japan urges China to stop attacks
"Japanese-made cars were randomly stopped, their drivers grabbed and thrown out... and the cars smashed and burned. The police and army seemed to do little to stop the riot," he said.
Tensions have been heightened this week after the purchase of some of the islands by the Japanese government from their private Japanese owners.
China briefly sent six surveillance ships into waters around the islands on Friday in response.
The islands, known as Diaoyu in China and Senkaku in Japan, are also claimed by Taiwan and have been a long-running source of friction in the region.
Analysts see Japan's decision to buy the islands as damage limitation in response to a much more provocative plan by the nationalistic governor of Tokyo, who wanted to purchase and develop the islands.
The dispute has been ratcheted up by the media in both countries - in China, where a leadership change looms and in Japan, in the run-up to an election.