The loud blast at Rafael, the weapons development arm of Israel's Defence Ministry, was heard across Haifa Bay in northern Israel. Ambulances raced to the scene.
Moshe Weizman, a regional police spokesman, said that "we are not talking about a suicide attack."
"It is a work accident. We don't know exactly what, a chemical that blew up in a bottle," he told Israel Army Radio.
Officials at Rafael declined comment.
Rafael makes sophisticated weapons, including missiles, tank armour and electronic warfare systems. Local fire officials said there hasn't been an accident at the site in the past 20 years.Reuse content