After Najib Abdul Razak failed to turn up at a 1MDB dialogue with NGOs today on security grounds, former premier Dr Mahathir Mohamad said he is prepared to debate the prime minister another time.

"If given the chance to debate, I will be happy to debate," he said when asked about the possibility of a one-on-one with the prime minister.

Najib failed to turn up at the event themed 'Nothing To Hide: The PM's Dialogue with NGOs', prompting the crowd which waited for almost two hours since 8am to become agitated.

In Najib's absence, Mahathir chose to make his own grand entrance as the angry crowd chanted 'Hidup Tun' (Long live Tun). Mahathir then proceeded to criticise Najib in his speech.

However, he was later stopped by police from speaking to the 2,000-strong crowd and proceeded to hold a press conference where he expressed readiness to debate Najib at another time.

In a statement, the Prime Minister's Office (PMO) had said Najib was prevented from attending the event at by police on security grounds.

Meanwhile, Perkasa chief Ibrahim Ali, who is a staunch Mahathir supporter, said a new debate should be held between Mahathir and Najib on television.

"I propose for a debate, a dialogue is not suitable in such a situation.

"If Najib is ready to face Mahathir, do it on television, we can watch at home in peace," he said.