It happened at Seabrook Brothers & Sons Inc. around 1:30 p.m. on the unit block of Finley Road in Cumberland County.
Crews began searching the facility and quickly assisted two of the approximately 150 employees. Cumberland County Administrator Kevin Smaniotto said one refused treatment and another was hospitalized for minor injuries.
Smaniotto said the incident caused a "minor" amount of ammonia to be released from the facility.
Update from officials on collapse at NJ food facility
"The levels of ammonia released are minimal. There is no hazard or threat to the community," he said.
Seabrook Brothers grows, processes, and freezes 150 million pounds of frozen vegetables.
Officials say workers use the ammonia to freeze the vegetables.
The view from Chopper 6 showed extensive damage to the property.
Crews on scene of partial roof collapse in Cumberland County, NJ
While 911 calls reported an explosion, officials don't believe there was any blast.
An official cause of the collapse is still underway.
Smaniotto said an emergency responder was also hospitalized for a possible heat-related illness.