Notorious crime boss Mahmoud "Brownie" Ahmad, 39, was shot dead outside a home in Sydney's southwest on Wednesday night.

Ahmad had been warned he was being targeted by a rival crime gang, with a rumoured $1 million bounty on his life, the Daily Telegraph reports.

The publication believes Ahmad had received several warnings from NSW Police, including a visit from officers just last week.

Ahmed had only returned to Australia after visiting Lebanon in early April, despite having knowledge of a potential contract for his death.

Police were called to Narelle Crescent in the southwest suburb of Greenacre around 9.30pm on Wednesday night after reports of multiple gunshots being fired.

Ahmad, 39, was found with gunshot wounds outside a home and died at the scene, with paramedics unable to treat him.

Up until a few months ago, the underworld figure was serving a six-year manslaughter sentence for the death of Sydney underworld figure Safwan Charbaji.

The broad daylight shootout occurred at Condell Park in April 2016.

However, Ahmad was able to get his sentence reduced to five years after helping authorities.

It's believed the shooter fled the scene after the incident. Photo / 7News

Detectives from the Homicide Squad will continue to investigate the circumstances surrounding the shooting, with assistance from the Bankstown Police Area Command, Southwest Metropolitan Region, and the Criminal Groups and Raptor Squads.

Police are also investigating whether two vehicles which were located on fire in Greenacre and Belmore are related to the deadly shooting.

Ahmad was the brother of slain underworld figure Walid "Wally" Ahmad, 41.

Wally Ahmad was gunned down in a spray of bullets after being ambushed outside the Centro cafe at Bankstown Central Shopping Centre in April 2016.

The father-of-six was hit with 11 shots fired from a pistol, seven of which struck him in the back and chest.

As of April 2020, the case was referred to the unsolved homicide squad.