The fire burned through the encampment on E Street South of Ventura Avenue in Downtown Fresno. The fire started around noon Wednesday.
Huge flames quickly charred several elaborate and poorly constructed shelters.
"Most of them, as you can see, are built out of highly combustible materials. They're in close proximity to each other. Plus the individuals that live in them need to heat their space they live in as well as cook food, that leads to open burning," said Lawrence French with the Fresno Fire Department.
The fire department responds to accidental fires in homeless encampments often. But this one investigators say is a case of arson.
"It does appear as though it was intentionally started and Fresno PD has detained on suspect and they believe there is an additional suspect is at large," French said.
Fire fighters say the flames quickly burned up the poles, dangerously close to high voltage power lines. PG&E responded to assist fire crews. The Central California SPCA was also called out to help with animals in the area.
Firefighters say small dog suffered burns. No cause has been determined but arson investigators are looking into several witness statements.
"There is a report that there is a fire bomb that took place. Until our investigators can confirm that, I'm going to say that the cause of the actual incident, other than it being intentionally set, we don't know what brought the ignition to the actual combustibles," French said.
The homeless camp where the fire occurred is just one of several the city says will be shut down. Last week the Police Department City Code Enforcement and Sanitation announced the closures.
The police department cites a sharp rise in criminal gang activity in the camps. Now the fire department is once again, pointing out another danger the homeless set ups pose to the public and first responders.