Malaysia: Hundreds detained over banned rally
Opposition activists are trying to gather supporters for a rally calling for electoral reform.
The police said the rally was illegal and that they would do everything they could to maintain order.
Major roads were blocked off and public transportation suspended from midnight on Friday (1600 GMT).
Riot police armed with batons and shields fanned out across the city, trucks mounted with water cannon were deployed and police helicopters could be heard overhead.
"The public is reminded not to be involved in any demonstration," a federal police statement said.
"Stern action will be taken against those who disobey."
A group calling itself the Bersih 2.0 coalition had been planning to hold the rally in a sports stadium on Saturday.
The opposition-backed rally comes amid increased pressure on Prime Minister Najib Razak for electoral reforms ahead of elections expected to be called next year.
Despite the crackdown, thousands of chanting protesters were still trying to reach the stadium from the different parts of the capital, carrying flags and balloons.
Activists said police fired tear gas on at least one group, while tense stand-offs were reported elsewhere; Kazinform cites BBC News.
To learn more go to www.bbc.co.uk