Six people are in a critical condition, among dozens of people injured when a man set fire to a Commonwealth Bank on Springvale Road in Melbourne's south-east.  The victims include children, adults, and the elderly.

Police said the suspect appears to be around 21-years old, and was seriously hurt himself.  He walked into the bank and used some sort of accelerant to light the fire.  "There's been apparently a flammable liquid used, I'm not sure what the flammable liquid was," Dandenong CFA operations officer Paul Carrigg said at the scene, explaining that it burst into flame with explosive force.

That much was seconded by the manager of a jewelry store across the road:  "I heard a loud bang - it sounded like firecrackers - there was smoke everywhere," Anthony Banh told Fairfax Media.  "A guy had severe burns on his face and arms and everything.  There was another man crouched on the ground with severe burns," he added.

There is some confusion about whether the victims were trapped in the burning bank by security gates that came down and blocked the exits. 

Monash Medical Centre called a "Code Brown" to deal with the mass casualty event; 13 patients were transported to the Clayton Hospital, including three children.  All are in a "satisfactory condition".  Another eleven adults were taken to Dandenong Hospital.

"One guy had both hands burnt, and was screaming and the paramedics and fire brigade were there," said witness Eric Fleuiot to the ABC.  "I just can't believe this has happened in Springvale."