Large anti-Japan demonstrations  took place Saturday afternoon in the cities of Xi'an , Chengdu  and Zhengzhou ; reportedly organized by university groups over the Internet through QQ and other social networking sites  [zh], the protests have taken many  [zh] by surprise. They come on the same day as an anti-Chinese protest was held in Tokyo, photos from which can be seen here .
[Update: China Media Project‘s David Bandurski has posted on the protests here . See update 2 below]
A large number of photos and tweets have come out of the protests, yet explanation as to what spurred them remains to be seen, however a Xinhua  report that came out soon after protests began references  the recent flare-up of the ongoing dispute  between the two countries over the Diaoyu islands . Despite having apparently been organized online, few blog posts regarding the motivation behind the demonstrations can currently be found, and even posts about related posts being deleted are being deleted .
Anybody know what sparked today's protests?
From Twitter around 5pm today, in Chengdu:
@carlwang87 : 春熙路的伊藤的玻璃被砸了，要不是警察围着，可能伊藤里面都被砸了
@carlwang87:  哎，游行的人看着就像混混似的，俺拿的索尼照的呢，当时怕怕
@carlwang87 : 就是成都香槟广场这，除了一个料理店被砸，还有一个打日本牌子的餐馆被砸，游行的起点也是这 他们转了一圈，回来把这砸了
@carlwang : 伊藤门口被警察围着，但是玻璃还是被人用东西砸了http://yfrog.com/mygfcwcj
@carlwang87 : 香槟广场人山人海，就是上面三楼一个日本料理被砸，二楼一个日本餐馆也被砸
Twitter user Henry Hu, who has uploaded to Flickr a large number of photos  from the Chengdu protest, has tweeted  a statement from the Chengdu city government which says that students from all major universities in the city were part of the protest. Among Hu's photos is one reportedly from the scene of the Zhengzhou protest:
From Xi'an, just between 5 and 6 pm:
@inxian : [西安散步]17点前后，钟楼附近的交通部分恢复了。最后一拨人马也开始沿南大街和西大街折返了。
@inxian : [西安散步]悲剧了！正要和平撤退的时候！钟楼饭店下的mizuno专卖店遭到袭击！钢化玻璃门被砸坏！有物品被焚烧！围观群众一片欢呼、鼓掌，并高喊抵制日货等口号。
@inxian : [西安散步]不只mizuno，tonywear，tonyjeans也遭殃了！他们高喊着抵制日货…
@inxian : [西安散步]里面的衣物被拉出，高高抛起…四处乱扔。然后焚烧！他们围着火堆，高唱的是国歌。然后鼓掌…
@inxian : [西安散步]西安钟楼附近现在重新集结了至少2万人。多名网友向inxian短信说：西安目前到处都是学生，到处拥挤堵塞！
@inxian : [西安散步]17点50分前后。这次人群是彻底散开了，因为防暴警察在后面催逼着。没有一辆公交车能看到钟楼附近，很多人都只好步行回家。
A photo on this BBS post  shows two police cars leading the Xi'an demonstration:
See here  for the latest Tweets regarding today's demonstrations.
And YouTube user luofeng0202 has uploaded video:
On Monday afternoon, yet another protest took place in Wuhan , in Hubei province. Among those live-tweeting it are Zhou Jian  and @hugh19871210  who put the number of protesters in the low hundreds and police at over a thousand.