The very act of public protest is unusual in China, but the anti-Japanese demonstrations that have raged there in recent days further the interests of the ruling party, so they're given a pass even though the official media plays down their size and violence.
The protests, which started on Saturday, came in response to Japan's arrest of a group of Chinese activists who had landed on a disputed island in the East China Sea last week. When a group of Japanese activists landed on one island in the archipelago claimed by both countries on Sunday, Chinese protests turned violent, with demonstrators reportedly smashing windows of sushi restaurants and Japanese-branded cars. According to The New York Times' Keith Bradsher, Martin Fackler, and Andrew Jacobs, the protests looked a lot more intense on social media than on state media:
The Chinese state news media portrayed the demonstrations as fairly small, each involving fewer than 200 people, and not extending to inland provinces. But photographs posted on Sina Weibo, the country’s most widely used microblogging service, suggested that the crowds had been far larger. In one photo said to be from the southwestern city of Chengdu, deep in China’s interior, the number of protesters appeared to be in the thousands.
In a country where protests are usually put down quickly and firmly, it's unusual to have state media reporting on public unrest in the first place. The Times reporters noted that "in the past, Beijing has allowed nationalist sentiment to bubble up into street demonstrations, but the authorities usually keep them contained out of concern they might spiral out of control or turn into popular antigovernment sentiment." In this case, protesters overturned a Japanese-branded police car in Shenzen, where it sounds like the action on the ground has gotten too intense for the state media to report.
For a good backgrounder on the dispute over the islands, which China calls the Diaoyu Islands and Japan calls the Senkaku Islands, check out Yale graduate student Joyman Lee's post on History Today, which includes this valuable context:
The dispute over the islands is a time bomb, given the enormity of the stakes involved. Despite Japanese claims that Chinese and Taiwanese interests in the islands are guided primarily by the possibility of major oil deposits, there has been little constructive dialogue between the countries involved in the question of the recent disputes over ownership of the islands. This remains at the very centre of broader tension between China and Japan, with the Nanjing Massacre of 1937 a focal point. Japan’s intransigent position on atrocities committed during the Second World War helps to fuel Chinese popular sentiment against it and makes the country an easy scapegoat for domestic discontent. Yet these days it is also easy to forget that China was the underdog for much of the 20th century; even today China is less articulate on the global scene than Japan