Banning vendors from selling alcohol in a district known as Little India from Saturday morning to early Monday, the Singapore Police Force declared the zone a "proclaimed area" under the Public Order Preservation Act.

The provision allows law enforcers to take action against anyone who consumes alcohol in the district, where some 400 South Asian workers went on a rampage that left 39 persons including police officers injured and 25 vehicles damaged or burnt last Sunday.

Local residents, shopkeepers and government ministers have said that alcohol may have been a contributory factor that triggered the riot.

"The suspension of alcohol sales and consumption is necessary to calm and stabilise the situation at Little India following last Sunday's riot and to prevent further public order incidents from occurring," the police said in a statement.

Thirty-one Indian nationals have so far been charged with rioting for their involvement and face up to seven years in jail and caning.

The riot erupted after an Indian construction worker was struck and killed by a private bus in the district, where migrant workers from South Asia usually congregate on Sunday by the tens of thousands to shop, dine and drink.

Activists have urged authorities to investigate whether the violence on Sunday was an indication of wider discontent among low-wage migrant workers.

Prime Minister Lee Hsien Loong has ordered the formation of a special committee to investigate the cause of the incident, Singapore's first riot since racial disturbances in 1969.

In its statement Thursday, the police said the suspension of alcohol sales and consumption will affect 374 "stakeholders and establishments" in the Little India district and its immediate vicinity.

"Eventually, police is likely to recalibrate the alcohol ban in a graduated and measured way," it said.

"Even after we have lifted the alcohol ban, there will in most likelihood continue to be certain restrictions on the sale of alcohol, and certain areas where alcohol consumption will not be allowed," it said.

The police have stepped up their presence in the district and installed an additional 26 street surveillance cameras in the aftermath of Sunday's riot.

The wealthy but tiny Southeast Asian nation of 5.4 million depends heavily on guest workers, with labourers from South Asia dominating sectors like construction.