Around 40 pounds (about 18 kg) of potassium nitrate were found in a two-story house in Queens, alarming police officials.
After firefighters arrived at the scene, they discovered materials at the site "that raised some concern", NYPD Deputy Commissioner John Miller said, as quoted by the New York Post.
ADVISORY: Please avoid the area of 19th Street and Astoria Park in Queens due to a @NYPDCT Bomb Squad investigation into hazardous material that was found inside of a house. Expect police presence and emergency vehicles in the area. More to follow. pic.twitter.com/nQIOR5dTEP— NYPD NEWS (@NYPDnews) September 16, 2020
"That included a number of chemicals, a number of packages, a number of books and manuals that caused them to call for investigators," John Miller said.
“There was no assembled device found, at this point,” Miller noted. “But I think the concern would be the individual chemicals that were found, and what they could combine to make,” he added.
The NYPD Bomb Squad and the FBI are investigating the incident.
Potassium nitrate, a compound commonly used as fertiliser, can also be used to make explosives; the Beirut blast which destroyed a large section of the Lebanese capital was caused by the detonation of 2,750 tonnes of ammonium nitrate, an industrial chemical which is also used mainly as an agricultural fertiliser.