The plot is the latest sign tensions are rising in Melbourne's underworld following a recent string of shootings, bashings and fire bombings targeting or linked to well-known gangland identities, including members of the Italian mafia and the family of slain drug kingpin Carl Williams.

The Sunday Age can reveal that detectives from the Purana​ anti-gangland taskforce have warned Mr Gatto his life was in danger after receiving intelligence about a conspiracy to have him killed.

Sources say the Colombian gang believes Mr Gatto was responsible for the disappearance of a cargo container from the docks they had imported as part of a smuggling operation.

Law enforcement authorities have long alleged Mr Gatto is a major player in the waterfront through his union connections and industrial mediation business.

Mr Gatto declined to comment on the allegations. "I have nothing to say except I don't have any enemies and I don't know anything about this."

It is understood that a close associate of Mr Gatto, who cannot be named for legal reasons, was also told by Purana detectives he was at risk of being killed. The man has been the target of two previous murder attempts. "I've got nothing to say," he told The Sunday Age.

Victoria Police has also declined to comment.

Mr Gatto was the target of numerous murder plots during Melbourne's so-called gangland war, which saw more than 30 people killed between 1995 and 2006.

In the most famous incident, Mr Gatto shot and killed hitman and Carl Williams associate Benji Veniamin in what a jury ruled was an act of self-defence.

Mick Gatto walks free from the Supreme Court after being acquitted of murdering Andrew Veniamin in a Carlton restaurant in 2004. Photo: Angela Wylie

But the threats continued even after the nominal end of the gangland war, with police intercepting veteran criminal Gavin "Capable" Preston in late 2011 ahead of what was believed to have been a plan to kill Mr Gatto that day. Preston, a suspect in the 2011 attempted murder of bikie Toby Mitchell, was recently convicted for the shooting death of ice dealer Adam Khoury.

This latest plot comes as sources say tensions are rising in Melbourne's underworld amid a recent escalation in violence, even if many of the incidents appear unconnected.

Since late 2013, a string of drive-by shootings and bashings have been linked to disputes involving Melbourne's Italian mafia.

In April, a close associate of Mitchell, Khaled Abouhasna​, was gunned down in the driveway of his Altona Meadows home.

More recently, the homes of Roberta Williams and George Williams, the ex-wife and father of slain drug kingpin Carl Williams, were targeted in shootings and arson attacks. A police officer was shot and seriously wounded as the assailants fled the scene.

Victoria Police has also formed a specialised squad to combat growing organised crime activity among a new, younger generation of criminals in the city's north west where the streets have been flooded with methamphetamine and guns.

Law enforcement officials have repeatedly attempted to dampen speculation that another major dispute in Melbourne's underworld is starting.

"It feels like there is something brewing out there," an underworld source said.

cvedelago@theage.com.au