A Facebook petition has seen more than 170,000 people back a call for Malaysian Prime Minister Najib Razak to quit, days after an electoral reform rally was broken up by police firing tear gas.

The page titled "100,000 People Request Najib Tun Razak Resignation" was set up on Saturday, the same day police arrested more than 1,600 people during the mass protest in the capital Kuala Lumpur.

Backed by opposition parties, electoral reform group Bersih 2.0 mobilised thousands of people to hit the streets in the biggest rally in four years, piling the pressure on Najib with elections widely expected next year.

Following the demonstration, the page attracted around 300 "likes" per minute, hitting its 100,000 target early Monday and the number has been steadily increasing with the page showing 172,868 "likes" on Wednesday morning.

"I don't understand why the harshness, the beatings (by police) and the tear gas," according to a post by supporter Sofie Muhammad on the page.

"The crowd didn't even throw stones at the shops, why is the government afraid? All we want is free elections."

Others felt the prime minister was too far removed from what was happening on the ground.

"Najib is out of touch. He cannot understand pain of tear gas, irritation of chemical water, pain of being kicked and beaten up by (police)," said Longyao Phang in another posting.

Bersih activists on Tuesday called for a royal probe into the electoral system, which the opposition says favours Najib's Barisan Nasional coalition, which has ruled Malaysia for half a century but saw its majority slashed in the previous general election, in 2008.

Opposition leader Anwar Ibrahim said the push by concerned democracy activists "augurs well for the future of this country."

"I would appeal to them to continue to monitor developments, exercise their right, have the courage of conviction to stand for what is right," he added.

Najib, who is in Britain on an official visit, has accused Anwar of masterminding the rally and manipulating its organisers to beef up support for his ambition to become the next prime minister.

The premier and his administration have faced previous online attacks with a Facebook petition in October calling for a million Malaysians to reject plans for a 100-storey megatower in Kuala Lumpur.

Malaysians are avid users of social network and micro-blogging sites.

A study by global research firm TNS last year showed Malaysians to be the most popular people on the Internet, with an average of 233 friends in their social networks compared with 68 in China and just 29 in Japan.