An explosive device detonated Tuesday outside an elementary school in Montana, authorities said.

No injuries were reported from the explosion at a playground at the Rossiter Elementary School in Helena, the Lewis & Clark County Sheriff’s Office said in a statement.

The device — a soda bottle with tape on it — blew up before the start of the school day, the Helena Independent Record said.

“We don’t know what time this thing exploded,” Undersheriff Jason Grimmis told the newspaper. “But what I do know is it did not explode while there was students there, while there was faculty there, which is a good sign.”

Anyone who finds a similar device should not touch it and should call cops immediately, Grimmis said.

All schools in the state’s capital city, as well as East Helena, initially were locked down after the incident as authorities searched those locations. The lockdowns were later lifted after the schools were cleared, KXLH reported.

Authorities were also conducting sweeps of other locations after the explosion, including inside the Capitol and other state buildings, the Independent Record said.

“We’re going through it methodically and slowly so we don’t miss something,” Sheriff Leo Dutton told the newspaper.

Several agencies, including the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives, are assisting local authorities in an ongoing investigation.

The NYPD’s Counterterrorism Bureau is also monitoring the situation, department officials tweeted Tuesday afternoon.