MALAYSIAN POLICE HAVE fired tear gas and chemical-laced water  at thousands of demonstrators demanding an overhaul in electoral policies that they call biased ahead of national polls expected soon.

At least 25,000 demonstrators swamped Malaysia’s largest city today in one of the Southeast Asian nation’s biggest street rallies in the past decade.

The demonstration reflected concerns that Prime Minister Najib Razak’s ruling coalition — which has held power for more than 50 years — will have an unfair upper hand in elections that could be called as early as June.

Activists have alleged that the Election Commission is biased and claimed that voter registration lists are tainted with fraudulent voters.

Demonstrators wearing yellow T-shirts poured into downtown Kuala Lumpur, massing near a public square that police had sealed off with barbed wire and barricades.

“I’m here because I’m a Malaysian and I love my country,” said information technology manager Burrd Lim. “There’s no election that’s perfect, but I want one that’s fair enough.”

Authorities said an opposition-backed pressure group that organised the rally had no right to use Independence Square, a symbolically important venue that hosts parades and high-profile celebrations.

The demonstration remained peaceful for several hours, with participants singing the national anthem, waving banners and chanting slogans.

Organisers declared the event a success and asked people to head home. But just as some were walking away, a small group appeared to suddenly breach the police barriers, prompting authorities to fire tear gas and water laced with stinging chemicals at portions of the crowd.