Tens of thousands of anti-Japan demonstrators rallied across China in protests over disputed islands, Tuesday, a key historical anniversary, as Tokyo said 11 Chinese government vessels had entered the area.

Some Chinese news outlets said the Chinese East Sea Fleet sent a number of nuclear-powered submarines to waters near the islands, known as Senkaku in Japan and Diaoyu in China.

Tuesday marked the anniversary of the Sept. 18, 1931 "Mukden Incident" in which Japanese soldiers blew up a railway in Manchuria as a pretext to take control of China's northeastern region, which is commemorated every year in China.

Japan’s Kyodo News said that anti-Japan rallies took place in 125 cities across China. The row intensified last week when the Japanese government bought three of the islands from their private Japanese owners, effectively nationalizing them.

Several thousand people gathered outside the Japanese embassy in Beijing, some throwing eggs and plastic bottles and others carrying portraits of Mao Zedong, the divisive late leader venerated by some for standing up to Japan.

Protesters carried signs reading "Kill Japanese," placards with the face of the Japanese prime minister on the body of a dog and a picture showing a Chinese soldier stabbing a Japanese one with a sword.

In the commercial hub of Shanghai, where about 17,000 protesters rallied outside the Japanese consulate, some carried banners reading: "Leave Japanese dogs" and "Exterminate the Japanese."

Japan’s NHK said 10 Chinese maritime surveillance ships and two fisheries patrol boat had entered an area known as the contiguous zone around the East China Sea islands, with three going into territorial waters.

Reports said the Japanese Coastguard dispatched a patrol boat armed with 40mm machine guns to the area.

The Japanese Coastguard is closely watching the situation as reports said that more than 1,000 Chinese fishing boats were headed toward the island group, according to Japanese media.