Protesters hurled stones, bottles and paint at the Japanese consulate in Shanghai and attacked Japanese businesses as thousands of people staged anti-Japan rallies.
Riot police, three-deep, linked arms to prevent the rowdy crowd on Saturday from entering the consulate as they yelled: "Go in, go in. Please let us in."
Police used loudspeakers to tell the crowd to disperse and while some people did, many remained at the site where the standoff was continuing.
An AFP reporter saw two people break through barriers surrounding the building, but they were pulled down by police. It was not known what happened to them.
Close to the consulate on Xianxia Road, four Japanese shops were attacked with bottles and eggs, another AFP reporter said. At least one window was smashed.
Onlookers estimated 5000 to 10,000 people marched along the main Yanan Road towards the consulate, yelling anti-Japanese slogans and calling for Tokyo to adequately apologise for its wartime aggression.
A duty officer at Shanghai public security bureau said the rally had not been approved.
"We received an application but did not approve it," she said.
The protests were sparked by the Japanese government's approval of revamped history textbooks that Beijing thought made light of the nation's atrocities in the second world war.
Last weekend, there were violent rallies in Beijing, and the southern cities of Guangzhou and Shenzhen.
"I hope no violent or illegal actions will be repeated. This is our sincere hope," Keiji Ide, spokesman at Japan's embassy in Beijing, said on Saturday.
The Japanese government has strongly protested at the new wave of anti-Japan demonstrations, saying Beijing should have prevented the violence.
"Even though information was available beforehand to infer that there would be a demonstration, nothing was done to prevent it... and we strongly protest to the Chinese government," Japan's Foreign Ministry said in a statement on Saturday.
It denounced the "destructive and violent actions" of the protesters and called anew for the Chinese government to prevent a recurrence.
"The end result is ... that this much damage occurred because proper security measures were not taken"
Japanese foreign minister
Foreign Minister Nobutaka Machimura was asked by reporters if he planned to cancel a trip to Beijing on Sunday.
"That option is not out of the question, but at present we are proceeding as planned," Machimura was quoted as saying by Akira Chiba, assistant press secretary at the ministry.
The statement on Saturday rejected Beijing's stance, saying such violence was not justified under any circumstances.
"The end result is ... that this much damage occurred because proper security measures were not taken," Machimura added.
Reports of threats and calls for caution surged in Japan on Saturday.
Kyodo News agency reported that an envelope containing white powder was sent to the Chinese Embassy in Tokyo on Friday. The contents turned out to be harmless, but police were investigating the incident as harassment related to the tensions.
Earlier, police said an envelope containing a razor blade was sent to the Chinese Consulate in western Osaka and that vandals dabbed red paint on the Chinese ambassador's residence in Tokyo.
"All these issues bring obstructions and restrictions to the deepening of bilateral cooperation and have the possibility of deteriorating the China-Japan relations"
Chinese state councillor
Chinese hackers are suspected of having launched cyber attacks on two Japanese government websites this week, and Kyodo reported on Saturday that Kumamoto University in southern Japan filed a criminal complaint with police over a similar incident.
Japan's Foreign Ministry has issued warnings to its citizens in China about possible danger, and Japanese businesses with major operations in China are taking precautions.
Japan on Wednesday said it would let its companies drill for oil and gas in the disputed East China Sea. Beijing, which began drilling in 2003, called the move a provocation.
"All these issues bring obstructions and restrictions to the deepening of bilateral cooperation and have the possibility of deteriorating the China-Japan relations," said Chinese State Councillor Tang Jiaxuan, a former foreign minister.
Protests are expected in other cities including Guangzhou, Shenyang, Chengdu, Hangzhou, Tianjin and Wuhan on Sunday.