It happened at 136 Spagnoli Road in Melville, the listed address for both the 110 Sand Company and Rason Asphalt, just before 1 p.m.
It apparently started as a fire, which caused a liquid asphalt tank to explode.
Officials said the fire was threatening two additional tanks.
"I was working at home...and all the sudden, I heard a huge blast, and it literally shook my house," area resident Barry Schwartz said. "It shook the floors to the extent my dog went wild."
Emergency crews were at the scene trying to contain the fire.
Authorities said no injuries were reported in the explosion.
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