Six people have died and 200 were injured in civil unrest in the Indonesian capital, its governor, Anies Baswedan, said on Wednesday.
Violence broke out after the election commission confirmed President Joko Widodo had won last month's election with a 55.5% share of votes against 44.5% for his opponent, former general Prabowo Subianto.
"As per 9 o'clock this morning, there were 200 people hurt being brought to five hospitals," the governor told broadcaster TVOne.
"The number of people dead was six," he said, adding that hospitals were conducting post mortems to determine the cause of death.
Prabowo has accused the incumbent president of systematic cheating but an election supervisory agency dismissed the claims, citing a lack of evidence. Independent observers have said the poll was free and fair.
Protests that started peacefully on Tuesday turned violent in the evening, forcing police to fire tear gas to disperse the crowd. Cars parked near an apartment housing the police's mobile brigade were set ablaze, media reported.
"As of now, police have arrested more than 20 people we thought were the provocateurs and who did other crimes," said police spokesman Dedi Prasetyo on Wednesday.
40,000 police and army personnel were on duty across Jakarta in a bid to maintain security, authorities said.