Former bikie boss Mahmoud "Mick" Hawi, once convicted of the Sydney Airport murder of Anthony Zervas before the charge was sensationally downgraded to manslaughter, has been shot in the face in a targeted attack in Sydney's south.

Hawi was ambushed as he sat in a four-wheel-drive inside the Fitness First car park on West Botany Street, Rockdale, just after midday on Thursday.

Paramedics performed CPR on the underworld figure as he was being rushed to St George Hospital.

Police said the shooter fled in a vehicle, which was last seen in Lindsay Street.

A crime scene has been established.

Police have also set up a crime scene on nearby Chandler Lane, where a vehicle, believed to be the getaway car, was torched and abandoned.

NSW Ambulance Superintendent Greg Price said Hawi was in cardiac arrest when paramedics arrived.

"Four paramedic units were on scene within seven minutes," Superintendent Price said.

"The patient was transported to hospital within six minutes from arrival on scene.

"The scene was very confronting for emergency service personnel. The paramedics performed their role to a high standard.

"I'd like to commend the paramedics and other emergency service personnel involved in this incident for their excellent work."

Reshan Muthukrishna has operated a physiotherapy clinic out of the gym for the past four years, where Hawi has previously been treated for a shoulder injury.

Mr Muthukrishna was seeing a patient inside the clinic when he heard "at least five" shots on Thursday.

"Around 12pm we heard some big bangs, we thought it was some equipment being dropped. I stayed in the clinic and my colleague ran out, it was just chaos," he said.

"Just pandemonium left, right and centre ... people on the scene were trying to help him, administer CPR."

Mr Muthukrishna said the shooting was "definitely not good for business" but "not unexpected or surprising ... [in] Rockdale," describing the Fitness First gym as a bit of a hub for gang members and bikies.

"Considering the history of this gym. There have been minor incidents with gangs and gang members training here," he said.

"He trained here, Mick trained here, him and his crew. He was a regular here, he used to come once or twice a day."

Mr Muthukrishna described the incident as "tragic" and added that the gym would now be closed for a few days while it remained a crime scene.

"I've got staff who are traumatised, so it's definitely not good for business ... obviously it will affect the clientele; Fitness First clientele, my clientele, this place has even more of a reputation than before."

In November 2011, Hawi was found guilty of murdering bitter rival Zervas, 29, who was bludgeoned with a bollard and stabbed in the chest and abdomen in the domestic departure hall on March 22, 2009.

Hawi, the then national president of the Comanchero motorcycle gang, was sentenced to a maximum of 28 years in prison with a non-parole period of 21 years.

But in 2014 the NSW Court of Criminal Appeal set aside the conviction and Hawi was subsequently allowed to plead guilty to the lesser charge of manslaughter.

He was sentenced to a maximum of six years and two months, with a minimum non-parole period of three years and six months.

He was released in 2015 to an address in regional NSW after the State Parole Authority granted his freedom subject to 22 conditions.

On Thursday afternoon, a police officer stood at the driveway to St George Hospital, stopping all cars and speaking to their drivers.

Multiple police cars, including four riot squad vehicles, were parked near the hospital's entrance. Riot squad officers were seen pacing up and down the footpath.

More to come