Twenty-seven men from South Asia were arrested in connection with Sunday night's riot in Little India, which apparently started after a bus ran over and killed an Indian worker as he was crossing a road.
Videos uploaded on social media within the hour of the accident, showed the private bus being set upon by an angry mob even as the 33-year-old victim's body remained pinned under the vehicle.
One man from the mob was seen in a video striking the windscreen and windows of the bus with a pole, while another tossed a litter bin at the vehicle from close range, shattering the front windscreen.
This even as the crowd continued to grow, cheering and shouting vulgarities in Tamil - turning violent in a matter of minutes, said eyewitnesses.
First responders to the accident, including a Singapore Civil Defence Force (SCDF) ambulance and a police patrol car, arrived at the junction of Race Course Road and Hampshire Road shortly after they received a call for help at 9.23pm.
SCDF rescuers were trying to reach the victim, who was trapped under the bus with hydraulic tools when the crowd apparently attacked them. "Projectiles were thrown at the SCDF rescuers while they were extricating the body," said a spokesman.
The mob spiralled out of control quickly after that, turning on the police, including the reinforcements who had arrived by then. "Some of the men lit beer bottles with fire and threw them at the police, I saw them throw more than 10 bottles," said Mr P. Kannan, who was waiting for a friend at the Little India MRT station.
Police estimates later put the mob at about 400-strong.
Commissioner of Police Ng Joo Hee said 300 police officers were activated to contain the rioters. These included men from the Special Operations Command (SOC) and Gurkha Contingent, who arrived at scene clad in anti-riot gear.
Residents living at Blk 661 Buffalo Road, many of whom had a bird's eye view of how the riot unfolded, said they saw at least three police patrols cars being turned onto their sides by the mob. Two ambulances at the scene were also attacked, one was seen with its windscreen smashed, while another, which was next to a Traffic Police Expressway Patrol, was on fire.
Said Mr Rohit Sodhi, 25, a service staff member at the Jungle Tandoor Restaurant: "I heard what sounded like bombs going off. Three times. Then I saw a huge mob running towards my restaurant and down Upper Dickson Road. The police chased them."
SOC officers, fanned out in anti-riot formation along the street, managed to break up the violent mob shortly after they arrived at the scene. Commissioner Ng said during a press conference after the incident, that the situation was resolved within the hour of the first call received.
"As far as we know now, there was no Singaporean involved in the riot," said Commissioner Ng. "The unwanted violence, rioting, destruction of property, fighting the police, is not the Singapore way."
Two police patrol cars and an ambulance were still ablaze when The Straits Times arrived at the scene. The burning vehicles triggered a few explosions before firefighters were at scene to put out the fire. A total of nine of SCDF and police vehicles were damaged in the incident, including an ambulance and three patrol cars that were burnt.
The SCDF said at press time that it had conveyed 18 casualties including four SCDF officers to Tan Tock Seng Hospital (TTSH) for treatment. The police said 10 of its officers were hurt during the riot.
The Straits Times understands that the driver of the bus was still undergoing an operation in hospital to treat a deep gash in his neck. His bus conductor was also hurt during the riot.
The incident came as a surprise to many, because not since the racial riots in Singapore in 1964, have the police been activated to respond to such unrest. Said 19-year-old polytechnic student Jovial Ng who lives on Buffalo Road: "We studied about the Maria Hertogh riots in social studies but we never expected to witness anything like this in real life."
Prime Minister Lee Hsien Loong in a Facebook post on Monday morning, called the riot a "very grave incident". "The situation is now under control, and investigations are underway. Whatever events may have sparked the rioting, there is no excuse for such violent, destructive, and criminal behaviour. We will spare no effort to identify the culprits and deal with them with the full force of the law.
"I urge all Singaporeans to stay calm. Do send the Police any information, photos or videos of the incident that you may have. I also wish the injured officers a full and speedy recovery."
When The Straits Times visited TTSH at about 1.45am on Monday, more than 10 SCDF officers were seen resting at a staging area, after receiving treatment for their injuries. Most had bandages to their face or arms, although one officer was in a wheelchair with a bandaged knee.
A nurse said roughly 15 SCDF officers arrived at about 1am for treatment at the hospital. Some family members of the injured were also spotted waiting at the hospital.
Mr Rafi Yaacob, 24, was at the hospital together with his mother and brother for his father, an SCDF ambulance driver, who had responded to the accident earlier.
The pest control officer said that rioters had smashed the windscreen of the ambulance his father was driving, and the glass shards had cut his face. His father was also injured when rioters threw stones at the paramedics.
Deputy Prime Minister Teo Chee Hean, who visited the scene after the riot with Second Minister for Home Affairs, Mr S Iswaran, urged members of public to stay calm and not react to speculation, and let the facts be ascertained.
"The Government will not tolerate such lawless behaviour," said Mr Teo, who is also Minister for Home Affairs. "I have asked Police to deal with all aspects of the incident, including the traffic accident, what happened immediately after the traffic accident, and all ensuing incidents."
Commissioner Ng said: "You can expect that we will make further arrest in the hours and the days that follow. Anyone with information about people who were involved in the violence last night should tell the police.
"We will go all out to find, to bring to custody, everyone who was involved in this incident."
Additional Reporting by Joyce Lim, Walter Sim, Lim Yan Liang, Kash Cheong and Lai Han-Wei.