(ROUGH CUT - NO REPORTER NARRATION) Indonesian police have arrested at least 20 people accused of provoking riots in Jakarta following official results showing President Joko Widodo had been re-elected, a police spokesman said on Wednesday.

Television footage on Wednesday showed smoke billowing from behind dozens of protesters who were dancing in the street in the Tanah Abang district of central Jakarta.

A separate crowd in front of the election supervisory body threw rocks at police, a Reuters witness said.

The General Election Commission (KPU) on Tuesday confirmed unofficial counts by private pollsters in the April 17 election, which gave Widodo a 55.5% share of votes against 44.5% for his opponent, former general Prabowo Subianto.

Widodo won more than 85 million votes of a total of 154 million cast in the world's third-largest democracy, but Prabowo told reporters he believed there had been widespread cheating and about 1,000 supporters gathered in Jakarta a day earlier.