Three police officers were fatally shot and two wounded Wednesday in southern Pennsylvania, and the shooter was killed by police, authorities said.

Law enforcement officers and emergency responders held a procession to honor the three slain officers Wednesday night.

The officers were at the scene, amid rolling farmland, to follow up on a domestic-related investigation that began the previous day.

It was one of the deadliest days for Pennsylvania police this century. In 2009 three Pittsburgh officers responding to a domestic disturbance were ambushed and shot to death by a man in a bulletproof vest.

The shooting erupted in the area of North Codorus Township, about 115 miles (185 km) west of Philadelphia, not far from the Maryland line, authorities said.

The two injured officers were in critical but stable condition at York Hospital, authorities said.

Authorities did not identify the shooter, the officers or which police department they belonged to, or describe the circumstances of how they were shot, citing the ongoing investigation.

AP video by Mingson Lau.