FARMERSVILLE, Texas (AP) — Two people were killed and three injured in an explosion Monday in an unincorporated area of Collin County, Texas, near Farmersville, officials said.

The deadly blast happened around 4 p.m. at Atmos Energy, a natural gas facility off Highway 78, according to WFAA-TV. Princeton and Farmersville fire departments, Collin County EMS and multiple other local law enforcement agencies responded to the blast.

The people involved in the explosion were contractors for Atmos Energy. The Collin County Sheriff’s Office said Monday night the contractors were employees of Bobcat Contracting and Fesco Petroleum Engineering. They were servicing a gas line in the area when the explosion happened, Farmersville police Chief Mike Sullivan told the station.

“Our prayers are with those who were affected by the events in Farmersville, Texas, today,” Atmos Energy said in statement. “Out of respect for their privacy, we are not releasing any names or additional details at this stage,” the statement added.

Two of the people injured were taken to a hospital.

Collin County Sheriff Jim Skinner said the explosion appeared to be an accident but he invited the FBI to assist in the investigation. It was not immediately known what caused the blast.