EMBATTLED Malaysian PM Najib Razak has poured scorn on a huge two-day rally that brought together thousands of protesters demanding his resignation.

Large crowd of protesters camped overnight on the streets of Kuala Lumpur wearing yellow shirts of the Bersih movement - a coalition for clean and fair elections - even after authorities blocked the organiser's website and banned yellow attire and the group's logo.

Former PM Mahathir Mohamad, who has been spearheading calls for Mr Najib's resignation, appeared at the rally with his wife for a second day, telling protesters that people power was needed to remove Mr Najib and return the rule of law.

Mr Najib has been fighting for political survival after leaked documents in July showed he received some 700 million US dollars (£455m) in his private accounts from entities linked to indebted state fund 1MDB.

He later said the money was a donation from the Middle East, fired his critical deputy and four other Cabinet members as well as the attorney general investigating him.

Police estimated Saturday's crowd at 25,000, but Bersih said the crowd swelled to 300,000 on Sunday from 200,000 on Saturday.

Mr Najib has slammed the protests for tarnishing Malaysia's image, and dismissed their size.

"What is 20,000? We can gather hundreds of thousands," he was quoted as saying by local media at a rural event in a northern state.

"The rest of the Malaysian population is with the government."

The rally was peaceful on Saturday and was scheduled to last until midnight Sunday to usher in Malaysia's 58th National Day.

"This is a watershed moment. Malaysians are united in their anger at the mismanagement of this country. We are saying loudly that there should be a change in the leadership," said protester Azrul Khalib, who slept on the street with his friends.

He said he was aware that the rally will not bring change overnight, but he wants to be "part of efforts to build a new Malaysia".