“We are not afraid as we know we are not in the wrong,” he said before a crowd of about 18,000 gathered outside the Kuala Lumpur City Centre shopping complex. He urged the people to topple the government, which he described as cruel.

Dr Mahathir, 91, also urged people to be brave, despite the risk of being imprisoned.

Police have detained 15 activists and politicians, including Bersih chairman Maria Chin Abdullah and Red Shirts leader Jamal Md Yunus.

Dr Mahathir told the crowd: “There is no jail that will be able to imprison all of us here today”, and then trained his guns on the Red Shirts movement, which he said were out to create chaos.

The arrest and subsequent remand of its leader Jamal, he said was nothing more than drama.

“They are trying to intimidate us, but you are strong people,” he said, adding that in all his 70 years in his political life, he had not seen a crowd as big as the one he witnessed today. Mahathir was prime minister for 22 years from 1981-2003.

He said that those who did not support the opposition were regarded as backing Najib Razak’s government.

“Maybe there are those here who still do not support any opposition party. So I implore you to join one today. Join Parti Pribumi Bersatu Malaysia who will collaborate with all opposition parties to bring down Najib.”

Mahathir is chairman of the party, formed this year after he left Umno.