Indonesia's capital Jakarta erupted in violence on Wednesday as police in riot gear fired water cannons and tear gas at protestors opposed to President Joko Widodo's re-election, with parts of the sprawling city littered with debris and burned-out cars.
The city's governor Anies Baswedan was quoted by local media as saying six people had been killed with more than 200 injured.
Police said they were probing reports of deaths, but denied that any live rounds had been fired on the crowd. Dozens were arrested.
Early Wednesday, some protesters had set market stalls and cars on fire, while hurling fireworks and rocks at authorities who had ordered them to disperse, said an AFP reporter on the scene.
The spasm of violence triggered fresh security advisories from the US and Australian embassies.
Later roads were blocked off in parts of the sprawling city, with some shopping malls, businesses and schools also closed.
More than 30,000 troops had been deployed in anticipation of unrest when the official poll figures were announced.
National police spokesman Muhammad Iqbal said 69 people had been arrested at the protests.
Authorities were also probing reports several demonstrators had died, including at least one reportedly killed by a bullet, he said.
But Iqbal said police had not fired live rounds, and portrayed the violence as a planned act by "provocateurs".
"The incident that happened this morning is not spontaneous, it was by design," he told reporters in Jakarta.
Iqbal would not confirm how many were injured or if anyone had died.
- 'Massive fraud' -
The violence came after Indonesia's election commission on Tuesday confirmed Widodo, 57, had beaten retired military general Prabowo Subianto for the presidency in a poll held on April 17.
Subianto has said he would challenge the results in court, and warned that his claims of widespread cheating could spark street protests.
Election officials and analysts have discounted his claims, but many supporters appeared convinced of fraud in the world's third-biggest democracy.
"I need to support the sovereignty of the Republic of Indonesia -- there has been massive fraud in this election," Puji Astuti, a 42-year-old Subianto supporter, told AFP at a rally in central Jakarta Wednesday.
Several allies of retired military man Subianto have been arrested recently, including a former special forces commander accused of smuggling weapons destined for the protests.
The protests in support of Subianto have sparked a backlash online from opponents with the hashtag #Tangkapprabowo (#ArrestPrabowo) trending widely on social media.
Wednesday's early morning violence happened after several thousand Subianto supporters rallied peacefully near the election supervisory agency's office in the heart of the capital on Tuesday.
The elections commission office was barricaded with razor wire and protected by scores of security personnel.
Tensions have also spiked since police said last week that they had arrested dozens of Islamic State-linked terror suspects who had planned to cause chaos by bombing protests.