Police across the country have started a massive seven-month crackdown to curb rising crimes and ease escalating social conflicts.

Known in Chinese as yanda, or "strike hard," the campaign is targeting extreme violent crime, gun and gang crime, telecom fraud, human trafficking, robbery, prostitution, gambling and drugs, the Ministry of Public Security announced on Sunday.

Police nationwide were also told to watch high-risk places such as suburbs, and to nip violence in the bud by being more vigilant to social conflicts and helping resolve problems.

"China, during a process of social and economic transformation, is facing emerging social conflicts and new problems in social security," Zhang Xinfeng, vice-minister of public security, told a national meeting on Sunday.

"Police at all levels must fully realize the complexity of the problem."

This is the fourth such round of yanda in China since 1983. During the campaign, police usually take tough measures against crimes and judicial authorities hand down swifter and harsher penalties.

The previous rounds in 1983, 1996 and 2001 were conducted while China faced high crime rates and complicated security situations.

Li Yunlong, a senior criminal law researcher at the Jiangxi Academy of Social Sciences, said the new crackdown comes amid rising crime and social conflict.

In one of the latest such cases on Saturday, a policeman in the Inner Mongolia autonomous region shot dead three civilians and injured a police chief. The suspect has been arrested and the motive remains unknown.

On June 1, a man in Hunan province equipped with three guns killed three judges in a court office out of revenge before killing himself.

The country has also witnessed a string of violence against primary school children this year, making public security authorities realize the urgency of the situation, Li said.

But Li stressed that all cases during the campaign should be carried out according to law. "The rights of suspects and criminals should be fully protected," he said.

He suggested that police better analyze the motives and reasons behind crimes.

"If a person has made up his or her mind to commit suicide after committing a crime, punishment is meaningless," he said. "Therefore, the most important thing is how to prevent crimes."

Li said it's essential to know the reason behind each crime and solve similar ones.

"But resolving social conflicts is not something police alone can achieve. It needs attention from all departments," he said.