Malaysian police fired tear gas and water cannons at more than 15,000 demonstrators who took to the streets to protest against controversial internal security laws.

In chaotic scenes in downtown Kuala Lumpur, some 5,000 police including riot squads arrested scores of protesters as they gathered at rallying points across the city, including two mosques and a shopping complex.

Deputy police chief Ismail Omar said that 175 people were arrested for taking part in the protest, aimed at pressuring the Government to abolish laws that allow for detention without trial.

"We just wanted to disperse them, so we used water cannon and tear gas to do that," he said, insisting the police action was not heavy-handed.

Among the detained were top opposition figures including R Sivarasa, vice-president of opposition leader Anwar Ibrahim's party.

Demonstrators played a cat-and-mouse game with police who attempted to prevent them from massing at the rallying points, darting into side streets before regrouping and marching through the streets.

At least 75 rounds of tear gas were fired and water cannons were unleashed at the Sogo shopping complex where the main crowd of some 10,000 people had gathered, intending to march on the royal palace.

As they began proceeding down a main thoroughfare, the police launched their sustained offensive which forced many to flee, coughing and choking from the effects of the gas.

Organisers said they wanted to present a 10-point memo to the king including demands for the abolition of the Internal Security Act, the closure of a camp where detainees are held, and an inquiry into all deaths in police custody.

At the national mosque, where an AFP reporter saw at least 50 detained, opposition legislator Siti Mariah Mahmud, from the Islamic party PAS, criticised the arrests of protesters as they attempted to enter the mosque.

"This is not reasonable. It's prayer time and this action is a breach of our religious freedom and duty," she said.

When prayers were completed, those who had managed to enter the mosque streamed out, joining a crowd of at least 5,000 which began marching before also being confronted by tear gas and water cannons.

There was traffic chaos in Kuala Lumpur, as trains stopped at affected stations and police roadblocks caused snarls that left many shoppers stuck in the city.

Prime Minister Najib Razak denounced the protest plans on Friday, saying it was unnecessary because he had agreed to review the ISA after coming to power earlier this year.

The legislation, a hangover from colonial days, has been used against Government opponents as well as suspected Islamist terrorists.

"We are here to fight for the ISA to be abolished," said Yati Ali, 45, one of some 100 women and children standing in a group outside the Sogo complex.

"We don't fear arrest. ISA is a cruel act, we are fighting for justice," she said.

- AFP