Three police officers were killed and two others critically injured in a shooting in the US state of Pennsylvania, while following-up on a "domestic-related" investigation, authorities have said, writes BBC.

Pennsylvania State Police Commissioner Colonel Christopher Paris said the gunman was fatally shot by the police. The incident happened just after 14:00 local time (18:00 GMT). Images from the scene showed a police officer being airlifted in a medical helicopter.

The shooting forced a nearby school district in Spring Grove, Pennsylvania - a small town of about 2,500 people - to briefly shelter in place. The district later said the school had not been affected. Officials said there was no active threat to the public.

The shooting happened in a rural area of York County in North Codorus Township, about 160 km west of Philadelphia. Authorities said officers were at the scene for an investigation that had begun the day before. Police have not shared many of the details because the investigation was ongoing, Commissioner Paris said.

Pennsylvania Governor Josh Shapiro reached the area on Wednesday afternoon and met the families of the officers killed, local media reported: "We grieve for the loss of life of three precious souls who served this county, served this commonwealth, served this country. This kind of violence is not OK, we need to do better as a society".