The Uyghurs are the indigenous people of Xinjiang and have been settled in the north eastern parts of China for centuries; the Hans are the majority ethnic group in the whole of China.
From my understanding of what's been going on, the Uyghurs have for a while, felt threatened by the Han's growing presence in their indigenous state of Xinjiang. The number of Han's residing in the state has more than tripled from the early 1900's as the region developed enormously in the manufacturing sector. Many Uyghurs feel disgruntled about not prospering with the development of the state capital -Urumqi, and feel that the Government has not done enough for them to prosper both economically and politically in the economic boom.
The more immediate causes for the Urumqi riots seems to have manifested from this long history of mistrust between the two ethnic groups. Reports covering the reasons behind the riots breaking out are still unclear: two Uyghur factory worker deaths and the rape of a Han woman seem to be the two most common stories.
Whatever the immediate cause, things do not look good for the people living in Urumqi. Uyghur and Han people in their thousands are fleeing for their lives, leaving behind everything in the need of safety.
Angry Uyghur women have been compelled to protest on the streets, carrying pcitures of their husbands/sons/brothers/fathers as they fight for their voices to be heard, hoping to be reunited with their loved ones.
Tension between the Uyghurs and the rest of China isn't something new. Many Uyghurs in the past have held a very pro-separatist attitude and have fought for their Independence to live in their own state, Turkmenistan; and although they succeeded in doing so, this success was very short lived as the Chinese Government dissolved the newly independent state, merging the Xinjiang province with China.
Pictures of Han men, strolling through Urumqi streets with cleaver's in hand, are all over the 'net. This particular picture sent a shiver down my spine >>
I just hope things settle down very soon as although the army's presence does seem to have brought a sense of calm amongst the riots, I doubt things will ever be the same again.