Alessio Di Giacomo, 22, who wasn’t at the factory at the time, heard the blast and rushed to the scene in the town of Città Sant'Angelo, the online newspaper Leggo reported.
His dad, Mauro, uncle, Federico and another relative, Roberto, are also believed to be dead.
"Unfortunately, we can only hope to find the remains of the three missing people,” Emanuele Cherubini, head of the medical rescue unit, said on Thursday night.
Another son, Gianmarco, is in hospital.
The Di Giacomo factory was the “pride” of industry in region, La Stampa reported.