Four people, including two police officers, were killed in a shooting in China's northern Hebei province on Tuesday, state television reported on its official microblog, a rare "mass shooting" in which five people were wounded.

The four killed in Suning county included at least one suspect, China Central Television said, giving few other details. The case was still under investigation, it said.

Media carried pictures of a news release from the government which said the 55-year-old male suspect was bipolar and that the shooting had occurred in a village, with at least two of the victims farmers.

The attack happened in the early hours of the morning, the news release said. It was not immediately clear if the official death toll included the suspect.

Gun violence is rare in China as firearms are tightly controlled and private gun ownership is restricted.

In December, an employee of China's central bank shot and killed two colleagues at the branch he was working at in the northeastern province of Liaoning.