KUALA LUMPUR, Malaysia – Police unleashed tear gas and chemical-laced water Saturday at thousands of demonstrators who staged one of Malaysia’s largest street rallies in years, demanding fair rules for national elections expected soon.

Malaysian police said 222 people were arrested.

Lawyers said most were expected to be released soon, but it was not immediately clear if they would be charged later with any offense.

Officials said three demonstrators and 20 police were injured.

At least 25,000 demonstrators swamped Malaysia’s largest city, 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.

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

The demonstration remained peaceful for several hours, prompting organizers 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.

Baton-wielding police backed by trucks mounted with water cannons sporadically fired tear gas at some demonstrators for at least an hour before much of the crowd was dispersed. People fled into streets and stores nearby, leaving shoes, bottles and other belongings scattered on the ground.