SINGAPORE—A rare riot here, staged by hundreds of workers from South Asia, is reviving public concern about the socioeconomic impact and sustainability of Singapore's heavy reliance on overseas labor.

Sunday's incident in Singapore's Little India district—a popular weekend hangout for South Asian expatriates and migrant workers—ended a riot-free period extending more than four decades and has blotted the city-state's image as one of Asia's safest countries. Analysts and labor activists say the unrest points to a growing challenge for policy makers trying to maintain social cohesion and curb antiforeigner sentiment amid festering tensions among its large migrant workforce.

Police and eyewitnesses say the riot started at about 9:30 p.m. after a bus hit and killed a 33-year-old Indian man. South Asian workers at the scene reacted by attacking the bus with sticks, stones and garbage bins, and later assaulted arriving police officers and paramedics, TV footage showed.

The violence was quelled by 11 p.m. by about 300 police officers—but not before injuries were inflicted on at least 39 law-enforcement and emergency-services personnel, as well as the driver and conductor aboard the bus in the accident. Dozens of police, emergency-services and privately owned vehicles were damaged, including five vehicles that were burned.

Public violence is virtually unheard of in Singapore, where public assembly is strictly regulated. But "incidents like this were, in a sense, waiting to happen," especially given the dense weekend crowds in Little India numbering in the thousands, said Hui Weng Tat, an economic professor at the Lee Kuan Yew School of Public Policy. Some migrants' resentment against perceived discrimination and poor working conditions could have contributed to the outburst, Mr. Hui said, adding that policy makers may need to consider improving migrant pay and treatment.