Torrid protests against Japan flared in Chinese cities for a second day on Sunday, with the government struggling to find a balance between venting public anger and containing violence that could backfire ahead of a delicate leadership succession.
The protests over islands claimed by both countries broke out in Beijing and other cities on Saturday, when demonstrators besieged the Japanese embassy, hurling rocks, eggs and bottles, and testing cordons of anti-riot police with shields and batons.
In other Chinese cities, demonstrators looted shops and attacked Japanese cars. Protesters also broke into a dozen Japanese-run factories in the eastern city of Qingdao, according to the Japanese broadcaster NHK.
The threat of fresh violence drew a warning from Japanese Prime Minister Yoshihiko Noda, who told Fuji TV that China "must strictly be on guard to prevent harm to Japanese citizens and companies", according to Japan's Kyodo news agency.
The protests, the latest setback in long-troubled relations between Beijing and Tokyo, followed Japan's decision on Tuesday to buy the disputed islands, which Tokyo calls the Senkaku and Beijing calls the Diaoyu and which could contain valuable gas reserves, from a private Japanese owner.
China called that decision a provocative violation of its sovereignty.
In the biggest flare-up on Sunday, police used tear gas and water cannon to drive back thousands of protesters occupying a major street in the southern city of Shenzhen, near Hong Kong.
A much smaller crowd, some throwing water bottles, resumed marching past the Japanese embassy in Beijing, now guarded by a six-deep cordon of anti-riot police.
"Japan, get the hell out of China!," some yelled.
Police used loud speakers to tell protesters that, while their anger was understandable, they should respect the law and remain "rational".
Crowds also gathered in the southwest city of Chengdu.
In Shanghai, about 1,500 people marched towards the Japanese consulate, although they were only allowed to enter cordoned-off areas in small groups. Protesters carried flags and images of former leader Mao Zedong as hundreds of police looked on.
The Nikkei business newspaper said on Sunday demonstrators had earlier attacked two Panasonic electronic parts plants in the eastern cities of Qingdao and Suzhou, and the company will decide whether to continue operations after checking the damage.
Toyota vehicle dealerships were also set on fire and many vehicles were damaged, it said, citing Toyota's China unit.
Domestic political preoccupations
The flare-up in tensions has come while both Beijing and Tokyo are focused on domestic political pressures, narrowing the room for diplomatic give-and-take.
Noda's government faces an election in months, adding to pressure on him not to look weak on China.
China's ruling Communist Party is preoccupied with a leadership turnover, with President Hu Jintao due to step down as party leader at a congress that could open as soon as next month.
While the public indignation against Japan could help to foster unity ahead of the succession, it has also exposed widespread public impatience for a tougher line from Beijing.
"I think it's time for the Chinese government to get tougher," a middle-aged Beijing man surnamed Xue told Reuters in front of the embassy late on Saturday.
"I don't mean war, but tougher action like sanctions. You can see how much Japan depends on our economy," he said.
Chinese state media praised "rational" expressions of anger but warned that violence could backfire against Beijing.
"There has been some irrational behaviour that is to be regretted," said a commentary on the website of the People's Daily, the main paper of the Chinese Communist Party.
"Raging expressions of patriotism will only bring joy to the (Japanese) evil doers, put our foreign policy on the defensive and wound the feelings of compatriots."
The territorial dispute escalated on Friday when China sent six surveillance ships to the group of uninhabited islets in the East China Sea. China's state-run media have issued a torrent of condemnation against Tokyo.
Despite their deepening economic ties, China and Japan have long been at political odds over bitter memories of Japan's military aggression in the 1930s and 1940s and present-day rivalry over disputed territory in the East China Sea.
Relations between Asia's two biggest economies chilled in 2010 after Japan arrested a Chinese trawler captain whose boat collided with Japanese coastguard vessels near the islands.
China's official Xinhua news agency said on Saturday big anti-Japan protests were also held in the Chinese cities of Xian, Changsha, Nanjing and Qingdao.
The protests could continue for days yet. On Tuesday, China marks its official memorial day for Japan's war-time occupation of China, which could provide a fresh focus for demonstrations.
Japan's newly designated ambassador to China, Shinichi Nishimiya, died in Tokyo on Sunday, the Japanese foreign ministry said. He had collapsed several days earlier.