Official sources state that the rioting began at around 2 a.m.,[19] and there were reports that they lasted until at least 4.30 a.m., when police arrived.[20] 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 batons and metal rods then responded; they called for backup using their phones.[11]