Authorities in Pennsylvania are asking the public to “be vigilant” after another explosion was reported Thursday, the latest in a string of mysterious blasts in the area over the past two months.

Pennsylvania State Police said in a news release a Milford Township road crew member was cutting grass along Brick Tavern Road, located about 40 miles northwest of Philadelphia, when the mower traveled over an object that “produced a sound similar to an explosion.”

“There were no injuries to the township worker and no visible damage to the tractor,” police said.

After getting off the tractor, the worker observed an area of the ground that was “disturbed.”

State Police released photos of the location of the incident, which showed a mower and a hole in the ground next to where the mower stopped, according to FOX29.

The incident on Thursday is believed to be connected with other events in Bucks County, where there have been more than 20 early-morning explosions since April 2.

“Our main goal is keeping the public safe and apprehending the subject(s) responsible for these events,” police said.

Police have previously said no one has been injured since the explosions began, but the events “disrupt emergency response personnel from their normal course of duty, straining local resources and impeding emergency personnel from responding to other calls for service.”

Residents across the area have reported booms loud enough to rattle windows and shake walls taking place between 1 and 4:30 a.m. and waking them up.

“It’s just like a boom. That’s just how it sounds,” Donna Weaver told FOX29 at the end of April.

Weaver, a resident of Quakertown, said she heard the booms several times over the course of the month, which woke her up in the middle of the night.

“I don’t know and it’s kind of scary,” she told FOX29. “Because I thought of thinking maybe it’s underground, maybe underground somewhere.”

Pennsylvania State Police are asking people to report “any suspicious items or activity” and those with information to call Lehigh Valley Crime Stoppers at (800) 426-TIPS.