Police in Malaysia have used tear gas and water cannons against thousands of people assembling for a banned protest in the capital Kuala Lumpur.
Police say they arrested some 1,650 people before the rally was broken up.
Opposition activists called the protest to urge the government to implement electoral reform.
The police threw up a cordon around central Kuala Lumpur from midnight on Friday, blocking major roads and suspending public transport.
Riot police armed with batons confronted the thousands of people who had slipped through the security net, dispersing them with volleys of tear gas.
Crowds around the city's main bus station were also hosed down by water cannons.
Opposition leader Anwar Ibrahim was one of a small number of people who were injured. He was taken to hospital after he fell to the pavement after a tear gas attack.
Protest leaders arrested
A group calling itself the Bersih 2.0 coalition had been planning to hold the rally in a sports stadium but the government of Prime Minister Najib Razak said the location was unsuitable and instead suggested a venue outside of the capital.
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BBC News, Kuala Lumpur
The confrontations between police and protesters come as a shock to many here who say Malaysia is a stable democracy.
The police had warned that anyone participating in this illegal march would be arrested to prevent chaos.
This demonstration started as a call for free and fair elections. But now analysts say it's a test of this country's fragile democracy.
Prime Minister Najib Razak has dismissed opposition allegations that the electoral system is plagued with fraud.
He blames opposition parties for trying to create chaos to generate political momentum.
In pictures: Malaysia reform protests
"Merdeka Stadium, which they chose, is too close to the city centre and can create massive traffic jams and disrupt businesses," federal police chief Ismail Omar was quoted as saying by the New Straits Times.
Instead, with roads closed and some public transport suspended, most shops shut on Saturday and the city remained empty apart from police and protesters.
Several leaders of Bersih, including Ambiga Sreenivasan and Maria Chin Abdullah, were among the 1,401 people that police said were arrested.
Most were expected to be quickly released.
Organisers of the rally said 50,000 people had come out, but analysts put the number at closer to 10,000.
The demonstration came amid a police crackdown on opposition figures.
Police have questioned more than 150 activists in recent weeks, and 91 have been barred from the city.
More than 30 activists remain in detention after being arrested almost two weeks ago.
Rally organisers say Malaysia's electoral system is plagued with fraud - they want longer campaign periods, automatic voter registration and equality of access to the largely government-linked mainstream media.
The authorities say the protesters are trying to promote communist ideology, thereby "waging war against the king".
Street protests are rare in Malaysia, but the police launched a crackdown after a similar demonstration in 2007.
Analysts say that protest helped the opposition win an unprecedented number of seats in the last general election.