 Official sources state that the rioting began at around 2 a.m. , and there were reports that they lasted until at least 4 @.@ 30 a.m. , when police arrived . An initial disturbance was reported at around 11 p.m. when security guards responded to a call for help by a female worker who felt intimidated by several chanting male Uyghurs . Two dozen Han workers armed with <unk> and metal rods then responded ; they called for backup using their phones . 
