The 81st anniversary of a Japanese invasion brought a fresh wave of anti-Japan demonstrations in China on Tuesday, with thousands of protesters venting anger over the colonial past and a current dispute involving contested islands in the East China Sea.

Outside the Japanese Embassy in Beijing, thousands shouted patriotic slogans and demanded boycotts of Japanese goods. Similar protests took place in Guangzhou, Wenzhou, Shanghai and other Chinese cities as the country marked the anniversary of a 1931 incident that Japan used as a pretext to invade Manchuria before World War II.

In many provinces, including Liaoning, Gansu, Yunnan, Sichuan and Anhui, local governments sounded sirens at 9:18 am to mark the Sept. 18 anniversary, the official China News Service reported.

For days, protests have been flaring across China, with occasional outbreaks of violence, including the torching and looting of Japanese-invested factories and shops. They have been the largest anti-Japanese demonstrations since 2005, reflecting ever-present anger toward Tokyo that periodically bursts to the surface.

China's authoritarian government rarely allows protests, and the wave of anti-Japanese demonstrations clearly received a degree of official approval.

In Beijing, streams of people marched past the embassy in orderly groups of about 150 people, herded by police who urged them to remain calm and peaceful. Some toted posters of Chairman Mao Zedong, and many shouted slogans such as: ``United, Love China, Never forget our national shame.''

Wang Guoming, a 38-year-old retired soldier and seller of construction materials, said he came to Beijing from his hometown of Linfen in Shanxi province to vent his frustration at Japan.

``I came here so our islands will not be invaded by Japan,'' said Wang. ``We believe we need to declare war on them because the Japanese devils are too evil. Down with little Japan!''

Metal barricades defended the embassy and rows of paramilitary police and SWAT teams lined the protest route.

Tensions have been growing for months in the dispute over ownership of East China Sea islands called the Senkaku in Japan and Diaoyu in China. The disagreement came to a head last week when the Japanese government said it was purchasing some of the islands from their private owner to thwart a Japanese politician's plans to buy and develop them.

China reacted angrily, sending patrol ships inside Japanese-claimed waters around the islands, which Tokyo has administered since 1972. Some state media urged Chinese to show their patriotism by boycotting Japanese goods and canceling travel to Japan.

Japan also has seen a surge of nationalism over the dispute. Its coast guard said Tuesday that it was questioning two Japanese who landed on one of the islands. Coast Guard official Yuji Sakanaka said it was unclear why the two landed.

A Coast Guard vessel issued a warning to a Chinese vessel near the islands early Tuesday. But officials said they could not confirm reports in Chinese state media that more than 1,000 Chinese fishing boats were headed toward the East China Sea island group.

Though there have been protests in many Chinese cities, turnout has been mixed. In Shanghai, just a few dozen protesters gathered at the downtown People's Square, where security was heavy.

Liu Qiming, 21, a recent college graduate looking for work, said he came after reading about the protests online and was committed to boycotting Japanese goods as a way of showing his solidarity.

``So far our government has been saying a lot but there's been no decisive action,'' Liu said. ``That's really a shame.'' (AP)