Authorities have released photos of two Australian nationals they would like to speak to after a Sydney underworld figure was shot dead in Vietnam.

Lorenzo Lemalu, 24, a senior leader of the notorious Coconut Cartel and former associate of the Alameddine crime family, was ambushed with bullets outside a restaurant in Ho Chi Minh City on Thursday night.

CCTV captured Lemalu's final moments standing with a group on a footpath along a busy dining strip before he was gunned down at point-blank range in front of shocked diners.

A second man was also wounded during the incident. 

Police in Vietnam have launched an investigation and released photos of two Australian nationals they would like to speak to.

Lang Kenny Trong Minh Do, 36, and White Justin John, 39, left Ho Chi Minh City in a taxi, before getting out near a supermarket in Tay Ninh, a town near the border of Cambodia, according to the police alert.

Their whereabouts are currently unknown. 

Police described the men as 'particularly dangerous' and urged the public to not approach them but report any possible sightings, according to local news reports.

There is no suggestion of wrongdoing by the men, only that police wish to speak to them.

CCTV posted online showed the moment Lemalu was gunned down in a busy dining precinct and followed into a restaurant.

As shocked diners ran for cover, another victim fell onto the road but managed to crawl onto the footpath.

He was then dragged into a restaurant by a bystander to get help.

Another man was seen crouching down next to Lemalu's bloodied body inside a restaurant, trying to render first aid while speaking to staff.

Another photo shows paramedics desperately working to revive Lemalu.

Lemalu was a former member of Proper 60, a western Sydney-based gang linked to the Alameddines led by Ali Younes aka Ay Huncho and had the group's name tattooed across his stomach.

It's understood Lemalu fell out with the Alameddines some time after fleeing Australia four years ago and began directing the Coconut Cartel's activities from South-East Asia.

The Coconut Cartel is a breakaway gang locked in an underworld crime feud with the Alameddines over control of the Sydney drug scene.

Photos emerged online last November of Lemalu eating a golden-leafed steak in Dubai, and was pictured in Albania just last month.

Messages obtained by SCN Worldstar and reportedly sent by members of the Alameddine network suggest they claimed credit for the execution.

'That's what happens when Coconuts try (and) fight the people that made them,' a message read.

But not everyone believes the execution is linked with the Sydney gangland wars, in the wake of a series of firebombings and drive-by shootings across the city in recent months.

'The big rumour is they ripped off some Albanians and that's why he was killed,' a gangster living overseas told the Daily Telegraph.

There are grave fears the killing was the latest chapter in Sydney's ongoing gang wars and could spark revenge attacks.

The latest execution happened just two nights after Alai Ahio, 28, a former associate of notorious rap group OneFour, was shot dead in what police described as a targeted attack in south-west Sydney.

He was at a Canley Heights home with four other men when they were ambushed by at least two attackers armed with guns and knives on Tuesday night. 

He was driven to Liverpool Hospital, where he died a short time later.

Four other men were also injured but survived.

The attackers fled the scene in a white SUV and remain on the run.