Turnbull takes Cambodia to task

Prime Minister Malcolm Turnbull has expressed concern to Cambodia's leader about the nation's crumbling democracy and human rights record while hundreds of expats protest at the ASEAN summit.

Mr Turnbull is hosting leaders from the 10-country Association of South-East Asian Nations and had bilateral talks with Prime Minister Hun Sen on Friday afternoon.

Cambodia is on a spiral towards authoritarianism following last year's ban on the main opposition party, the arrest of opposition leader Kem Sokha and the forced closure of an English-language newspaper.

The opposition party had been poised to strongly challenge Hun Sen's 33-year rule at the July election.

Mr Turnbull insists Australia has "frank engagement" with all ASEAN countries.

"We approach ASEAN with the greatest respect. We respect the consensus model on which it is based and we will be discussing issues of every description," Mr Turnbull told reporters.

It's understood the prime minister raised the importance of democracy, human rights and the upcoming Cambodian elections with Hun Sen during their meeting.

The pair also talked about trade and economic engagement, peacekeeping and the threat posed by North Korea's nuclear weapons testing program.

Meanwhile, hundreds of Cambodian expats rallied in Sydney's Hyde Park on Friday afternoon, protesting against Hun Sen's visit to Australia.

Before his visit, the Khmer prime minister had threatened to beat up any protesters who burnt effigies of him in Sydney.

Protesters carried signs accusing Hun Sen of being a "human rights violator" while chanting for an end to his violent crackdown on political dissidents.

One group of protesters told AAP they felt a duty to protest his visit regardless of his threats.

Others urged Prime Minister Turnbull not to "make deals with the devil" while meeting the Cambodian leader.

Protester Bou Rochana's husband Kem Ley was murdered in a suspected political assassination.

She and her five children were granted refugee status and moved to Melbourne last month after 15 months in limbo in Thailand.

Ley was gunned down in 2016 after he made comments critical of the prime minister's business dealings.

"Justice for Ley," a sign in the crowd read.

Former foreign minister Gareth Evans, who helped bring peace to war-torn Cambodia in the early 1990s, last week said the "manifestly indefensible" refugee resettlement deal had compromised Australia's response to the Cambodian situation.