The fire broke out in the basement of the building, which contained both residential and commercial units, just before 5:30 a.m. and quickly spread through the first-floor store on West 2nd Street.
The flames then burned through the home above and out the roof, which eventually collapsed.
Four people who lived in the home escaped without injury. Firefighters were pulled out before the collapse.
The Plainfield fire chief says firefighters were hampered by propane and acetylene gas inside the vacant building that was feeding the fire. PSE&G workers arrived and were forced to dig up the street to shut down the gas line to the building.
Firefighters initially had trouble getting water on the fire, and stretched fire lines from hydrants blocks away.
They finally got control of the fire around 7 a.m.
The cause is under investigation.
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