Detectives from the Arson and Explosives Squad are investigating following a fire at a Chapel Street tobacco store overnight.
Emergency services were called after witnesses observed a number of males pouring accelerant inside the premises, before it was set alight around 4.15am.
The group then fled the address in a waiting vehicle, with one of the group visibly on fire.
Nobody else was inside the premises at the time.
The store sustained extensive damage during the incident, as well causing damage to surrounding businesses.
Emergency services were called to an address in Fitzroy shortly before 5am after reports of a male with significant burns to his body.
A 51-year-old man was conveyed to hospital where he remains in a critical condition.
A crime scene has been established and an arson chemist will attend the scene today.
Investigators also believe an attempted arson at the same store on 6 December last year is likely linked.
The investigation remains ongoing.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential report online at www.crimestoppersvic.com.au
Quotes attributable to Detective Inspector Chris Murray, Arson and Explosives Squad:
"We have been clear since these arson attacks started that it was only a matter of time before someone is killed or very seriously injured as a direct result of one of these fires. Today is that day.
"The only thing we can be thankful for is that it wasn't an innocent member of the community injured.
"Fire is absolutely uncontrollable and unpredictable, and the sheer recklessness of this offending is just abhorrent.
"If there is anyone out there who witnessed the fire or has any information at all about who is responsible, then I urge those people to come forward and tell us before this happens again with potentially fatal consequences."
