KUALA LUMPUR, Sept 21 (AFP) - Malaysian riot police fired tear gas and water cannon Monday to clear chanting supporters of deposed deputy premier Anwar Ibrahim outside the main Kuala Lumpur courthouse.

About 30 people were detained and police were seen kicking and beating one man carrying a Malaysian flag who was hauled away, a witness said.

More than 1,000 people had been outside the court waiting for an appearance by Anwar, who was detained Sunday night after police stormed his home.

Six truck loads of riot police had been outside as supporters chanted slogans in favour of Anwar and calling for Prime Minister Mahathir Mohamad to stand down.

Police, some armed with automatic rifles, gave several shouted warnings for the crowd to disperse but were ignored, an AFP reporter at the scene said.

After an officer shouted ''this is the final warning,'' one water cannon truck opened opened fire. Riot police fired also let off three volleys of tear gas.

Running clashes then ensued before the water cannon was used again.

Around 30 armed riot squad police moved up the road outside clearing the crowds, beating batons on their shields.

But groups of supporters shouting ''reform, reform'' and ''long live Anwar" regrouped and taunted the police.

A group of about 30 detained supporters were seen in a police truck outside the court. Two had been men who ran along the street waving Malaysian flags.

As a police helicopter hovered overhead police made new warnings for the crowd to disperse through loud hailers. As the disturbances continued the water cannon was used again.