Police fired water canon and tear gas to disperse tens of thousands of protesters in the Malaysian capital Kuala Lumpur.
The demonstrators converged on Independence Square to demand electoral reforms in defiance of government legislation banning such gatherings.
Police claim they were forced into adopting aggressive tactics when protesters attempted to break into the central square.
The ruling party has been in power for 55-years with Prime Minister Najib Razak expected to call an election for June.
Many believe a violent response by the police could hurt the government as middle-class voters become disillusioned with the regime.
Last year a heavy handed reaction to a similar protest saw Razak’s approval rating plummet.