MEXICO CITY — A police helicopter has crashed in the Mexican border city of Tijuana, killing at least two officers.

The prosecutor’s office in Baja California state identified the dead as a police captain and the helicopter pilot. It’s not immediately clear what caused the crash.

The chopper was reportedly assisting in a search for criminal suspects when the accident occurred Wednesday.

Also Wednesday, state officials said three houses tumbled 15 meters (45 feet) into a collapsed building site excavation in the northern city of Monterrey. A local official told Milenio television that at least one person died.

The government of the state of Nuevo Leon said rescue personnel were searching for other possible victims on Thursday.