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.

“The independent Elections Commission has gone to extraordinary lengths to ensure that the next elections are free and fair and meet the highest international standards,” Dato’ Seri Hishammuddin Hussein, minister of home affairs, said in a statement.

‘Ruthless regime’

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.

Lawyer Malik Sarwar tells Al Jazeera demonstrators should have been allowed to protest peacefully

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.

Rachel Chia, a Malay resident, told Al Jazeera: “Free media is also one of the demands of Bersih. We don’t have that here, our newspapers print lies and our news portals give us filtered information. They only print and show the people what they want us to know.”

Another resident, who asked not to be named, told Al Jazeera: “When I see the hundreds of thousands of angry protesters storming the streets of Kuala Lumpur and yet not even one shop is looted, not even one trash bin is burned, I know we who are powerless are stronger than the armed forces … I am witnessing the beginning of the end of a ruthless regime.”

At least 222 people were reported to have been detained by the authorities.

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.

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.

Al Jazeera’s Harry Fawcett, reporting from the city using the Skype for iPad application, after Malaysian police “busted” his crew’s camera, said he witnessed police “kicking, slapping and punching” several protesters.

Defending the police, the minister of home affairs, said: “I would like to commend the police for their professionalism and the restraint they have shown under difficult circumstances.”

According to Malaysian police, as many as 222 people were arrested at the rally

“A group of protesters tried to provoke a violent confrontation with the police, but overall at this stage it would seem this afternoon’s protest passed off without major incident,” he said.

“Despite opposition claims to the contrary, the government fully respects peoples’ right to peaceful protest, which is enshrined under Malaysian law.”

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.

According to our correspondent, 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.”

Our correspondent adds that as far as the protesters are concerned, the government has not 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,” he said.

‘Greatest democracy’

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 had a dismal showing against the opposition in 2008, and Najib is under pressure to improve on that.

Follow Ayse Alibeyoglu on Twitter @aysealibey