"Nobody would be allowed to sell or consume alcohol in approximately 1.1 sq km zone declared as "proclaimed area" for the weekend under the Public Order (Preservation) Act, said Deputy Commissioner of Police, T Raja Kumar.
Anyone who is drunk or disorderly in the area can be arrested for being a public nuisance, he said.
"But some may not have realised it because the news of the ban hasn't percolated down to the last person. Our officers will tell them, if you are cooperative and throw away the alcohol or walk out of the area, that is fine," the Singapore daily Strait Times quoted T Raja Kumar as saying.
A joint statement from Singapore's Manpower Ministry and Land Transport Authority (LTA) has highlighted the need "to calm and stabilise the situation" following last Sunday's riot.
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The ban would allow police to assess the next step in consultation with the various stakeholders for a more permanent intervention to ensure that a repeat of last Sunday's riot does not occur, and to restore the sense of safety and security for residents, shopkeepers, visitors and others in the area, said the statement.
The riot left 39 Home Team officers injured and 25 police and Singapore Civil Defence Force vehicles damaged.
The LTA has also suspended 25 private bus services on Sunday which ferried thousands of men to Little India where they usually spend their days off.
Singapore has imposed such blanket ban for the first time on an area following the worst riot in the last 40 years.