Hundreds of Rohingya refugees from Myanmar left a Malaysian detention center on Wednesday when a riot broke out, police claimed, with six dead on a highway as they fled.

Many Rohingya arrive in Malaysia by boat following arduous, months-long maritime voyages. Those apprehended are frequently transported to detention centers, which rights organizations allege are overcrowded and filthy. According to Khairul Dzaimee Daud, the country’s immigration head, 528 Muslims fled a center in northern Kedah state about 4:30 a.m. (2030 GMT Tuesday).

Most were immediately apprehended, but 176 remained at large as of Wednesday afternoon, according to authorities. After the disturbance broke out, the migrants pushed through a door and obstacles at the center, leaving the 23 guards on duty unable to handle the situation. According to authorities, six of the detainees—two adult males, two adult women, one child, and one boy—were slain when they attempted to cross a highway after fleeing.

According to authorities, the reason of the disturbance and break-out is being investigated. The missing inmates are being sought by police, personnel from other agencies, and members of the public.

Malaysia, a relatively prosperous Muslim-majority country, is a popular destination for Rohingya refugees fleeing persecution in their largely Buddhist homeland or refugee camps in Bangladesh. More than 100,000 Rohingya dwell on the country’s outskirts, working illegally in construction and other low-wage professions.