An explosion occurred at 7:30 p.m. in a Shell Loading unit of an ammunition plant. The initial explosion triggered a fire and subsequent series of explosions which continued for three days. About 62,000 persons were evacuated. Shells projected into the air exploded in the plant ammonium storage depots : 4 000 t of ammonium nitrate exploded, leaving huge craters. The facility, said to be one of the largest in the world at the time, was destroyed along with more than 300 buildings, forcing reconstruction of South Amboy and Sayreville. Damage to the area was estimated to be US $18 million and the area has long been littered with unspent shells that were still found during digging works in 1997.

The cause remains unclear. Initial reports blamed the explosion on an accidental spark, company negligence and German sabotage. Sixty-four residents and employees died from the explosion.