Construction on a Jersey City building has been stopped after crews improperly used chemicals in an attempt to break up rocks.

Jersey City spokesperson Jennifer Morrill says that the incident happened at 191 Academy St., which is under construction. She says that the Building Department had shut down the construction site earlier Thursday and cited them for not protecting the adjoining property from work they were doing with a jackhammer.

Morrill says that the construction crew then apparently placed a chemical into drilled holes in the ground in an attempt to break up rock. They did this without authorization from the Building Department, according to Morrill.

Morrill says that the chemical reacted to the heat outside, causing smoke and rocks to eject from the holes. No one was hurt, but one building did have a window hit by one of the rocks.

The Jersey City fire and police departments are now monitoring the construction site.

The construction crew was also issued a stop work order at the site, as well as other violations, according to Morrill.