Former Malaysian leader Mahathir Mohamad, joining anti-government protesters for a second day on Sunday, called for a "people's power" movement to topple Prime Minister Najib Razak over a financial scandal.
"The only way for the people to get back to the old system is for them to remove this prime minister," said Mahathir, a deeply respected 90-year-old who was once Najib's patron and is now his fiercest critic.
"And to remove him, the people must show people's power. The people as a whole do not want this kind of corrupt leader," he told media before heading to the rally, whose numbers police estimated at 25,000 on Sunday afternoon.
The protest has brought into the streets a political crisis triggered by reports of a mysterious transfer worth more than $600 million into an account under Najib's name.
Najib, who denies wrongdoing, has weathered the storm and analysts say the protest is unlikely to inspire broad public support for him to quit because it lacks a strong leader.
These protests, unlike the 2012 rally, also lack the support of a party identified with the Malay majority: most protesters were from the minority ethnic Chinese and Indian communities.
However, Mahathir— the country's longest-serving leader—was a leader of the ruling United Malays National Organisation (UMNO), which represents Malays.
UMNO Vice-President Hishammuddin Hussein said that by turning up unexpectedly at the anti-government rally on Saturday, Mahathir had "crossed over the line."
Another UMNO leader said a million government supporters would stage a "red shirts" rally on Oct. 10 that would trump the protests of the past two days.
"This shows the solidarity of Malaysians, that Najib still has the majority support," Jamal Yunos told Reuters.
Mahathir's siding with protesters sits oddly with the often-authoritarian style of his own 22-year rule until 2003, during which Malaysia became a powerhouse of economic development but also won a reputation for cronyism and dubious "mega-projects".
Najib was once a protégé of Mahathir, just as the now-jailed Anwar Ibrahim — once widely viewed as Mahathir's heir apparent—was before him. Anwar fell from favour when he began a popular "reformasi" (reform) movement against the graft and nepotism he said marked Malaysia's business and political worlds.
Mahathir sacked him from his posts, and charges of sodomy and corruption followed. Mahathir has always maintained that the sodomy charges were genuine and made Anwar unfit to be leader.
On Sunday, security remained tight and anti-riot trucks stood ready, but there were no reports of violence.
City authorities rejected an application by pro-democracy group Bersih for a protest permit, which had raised fears of a repeat of a 2012 rally when police used water cannon and teargas to disperse protesters.
In a sign the government was losing patience, Deputy Prime Minister Ahmad Zahid Hamidi warned organizers they could face legal action. "They must face the consequences if they dare to break the law," he said, the New Straits Times reported online.
The national news agency Bernama said 12 people in the southwestern city of Malacca were arrested for wearing the signature yellow T-shirts of the protests, which the government had banned before the rally.
A nation of 30 million, Malaysia is predominantly Malay Muslim with significant Chinese and Indian minorities. Its ambitions to rise from a middle income to a developed nation this decade have been stymied by slow-paced reforms and Najib's increasing authoritarianism.
Concerns over the political scandal partly contributed to the Malaysian currency plunging to a 17-year low earlier this month.
1MDB, set up by Najib in 2009 to develop new industries, has accumulated 42 billion ringgit ($10.1 billion) in debt after its energy ventures abroad faltered.
Support for Najib's National Front has eroded in the last two general elections. It won in 2013, but lost the popular vote for the first time to an opposition alliance.
Apart from Najib's resignation, the demands being sought are institutional reforms that will make the government more transparent and accountable