Thousands of demonstrators demanding free and fair elections met with tear gas and water cannon in capital Kuala Lumpur.
Malaysian riot police have fired tear gas and used water cannon on a crowd of demonstrators who staged one of the country's largest street rallies in years, demanding fair rules for national elections expected soon.
At least 25,000 demonstrators swamped Malaysia's capital Kuala Lumpur on Saturday, hoping to pressure Prime Minister Najib Razak's ruling coalition - which has held power for nearly 55 years - to overhaul electoral policies before polls that could be held as early as June.
Authorities insist the elections will be free and fair, rejecting activists' claims that the Election Commission is biased and that voter registration lists are tainted with fraudulent names.
Demonstrators wearing yellow T-shirts, waving banners and chanting slogans poured into downtown Kuala Lumpur, massing near the city's historic Merdeka (Independence) Square that police had sealed off with barbed wire and barricades.
Authorities had refused to allow Bersih, or Coalition for Free and Fair Elections - the opposition-backed pressure group that organised the rally - to use the square, a nationally renowned venue that hosts parades and patriotic celebrations.
The demonstration remained peaceful for several hours, prompting organisers to declare it a success and ask people to head home.
But when a small group appeared to suddenly breach the police barriers, authorities began firing tear gas and water laced with stinging chemicals at the crowd.
Authorities detained dozens of people, with Malaysian media reports saying as many as 60 were arrested.
No major injuries were immediately reported.
Police action 'unjustified'
Kuala Lumpur's police said in its social media statements that authorities were forced to move against the protesters, but opposition leaders and rights groups said the action was unjustified.
A federal police spokesperson estimated there were about 25,000 demonstrators, but many witnesses and some Malaysian news organisations said there were between 80,000 and 100,000 protesters at the rally.
The rally's organisers have also sought longer election campaigning periods and changes to ensure citizens living abroad can cast ballots, as well as international observers for the polls and fairer access for all political parties to the government-linked media.
Al Jazeera's Harry Fawcett, reporting from Kuala Lumpur, said: "As far as the protesters are concerned, the government haven't met their demands. They want a series of improvements to the electoral system. They are calling for better electoral role. They also want the electoral commission, which runs elections this country, to be entirely reformed.
"The protest was not what both sides [government and protesters] were talking about. They were talking about peaceful protests. Ideally, the protesters wanted to protest inside Independence Square."
Saturday's gathering follows one crushed by police last July, when 1,600 people were arrested.
That rally for clean elections prompted a police crackdown with tear gas and water cannon.
A resulting backlash prompted Najib, Malaysia's prime minister, to set up a parliamentary panel whose eventual report suggested a range of changes to the electoral system.
But Bersih and the opposition are demanding a complete overhaul of a voter roll considered fraudulent and reform of an Election Commission they say is biased in favour of the governing coalition.
Najib has launched a campaign to repeal authoritarian laws in a bid to create what he called "the greatest democracy".
His ruling coalition has governed Malaysia for more than five decades but made a dismal showing against the opposition in 2008, and Najib is under pressure to improve on that.