Thousands of protesters gathered in Kuala Lumpur on Saturday for a two-day rally to demand the resignation of Prime Minister Najib Razak, bringing to the streets a political crisis over a multi-million-dollar payment made to an account under his name.
The Malaysian leader has weathered weeks of attacks since it was reported that investigators probing the management of debt-laden state fund 1Malaysia Development Berhad (1MDB) had discovered the unexplained transfer of more than $600 million.
Protesters hope to spark a people's power movement forcing Najib out, but political analysts doubt he will be toppled.
Security was tight as the rally got under way and access to a square where the protesters plan to converge was blocked.
The Malaysiakini news portal said 10,000 people had gathered by early afternoon but police estimated the crowd at half that number. Some members of the crowd had started to walk towards the square, Reuters witnesses said.
Read More1MDB sparks political crisis
Protesters carrying "Out, Najib, Out" placards sang the national anthem, honked plastic horns and shouted "bersih!", a Malay word for "clean". Bersih is also the name of the pro-democracy organisation behind the rally in Kuala Lumpur and the two main cities on Malaysia's side of Borneo.
"We the Malaysians want to clean up this country, we reject dirty politics," said Tinagar Veranogan, a demonstrator in a crowd of predominantly young people as a helicopter buzzed overhead.
The Star daily said on Thursday the army could intervene if the protest gets out of hand and a state of emergency is declared. A military spokesman declined to comment.
Kuala Lumpur authorities rejected an application by Bersih for a protest permit, raising fears of a repeat of a rally in 2012 when police used water cannon and teargas to disperse protesters. Reuters journalists saw several anti-riot trucks and a water cannon parked near the Merdeka Square on Saturday.
The government has blocked access to Bersih's website and banned wearing of its signature yellow T-shirts under an order prohibiting material prejudicial to public order and security.
The anti-graft movement Transparency International called on the Malaysian government to respect the right of citizens to demonstrate peacefully without fear of reprisal.
The government "should listen to the concerns of its people", organisation chief Jose Ugaz said.