A police officer in South China was detained on Monday on allegations of shooting and killing a pregnant woman.

The incident is the fourth case in the past two years of a police officer being accused of using an issued firearm to kill innocent people, and has reignited a debate on police abuse of guns.

Authorities say the incident happened at 10 pm in a restaurant in Guigang, in Guangxi Zhuang autonomous region.

The suspect, identified as Hu, is alleged to have shot the restaurant's owners, Cai Shiyong and his wife, Wu, police said.

Wu, who was five months pregnant, was shot once in the stomach and once in the head, according to media reports.

Police said the officer was intoxicated and had a dispute with the victims. However, in an interview with Beijing Youth Daily, Cai denied this.

He said Hu arrived and asked if the restaurant sold milk tea. When he was told it did not, he threatened two customers with his gun and then shot the couple.

The report added the suspect was not wearing his uniform at the time, and witnesses said he was accompanied by two others who left in a white car.

Police did not confirm whether the suspect was on duty.

A similar shooting happened in Laibin, near Guigang, on July 21, 2011.

Tan Ningjiang, a police station chief in the city, shot one person dead and wounded another while drunk.

Last year, there were two cases in Shenzhen, Guangdong province, in which police officers shot and killed civilians.

In one of those, policeman Li Caikun falsely claimed a robbery had taken place and got a street vendor to file a police report. On the pretext of the false claim, Li fatally shot the victim, surnamed Ban, on July 1, 2012.

Li was given a two-year suspended death sentence after the court found he killed Ban because of an argument during a previous encounter at Li's police station in the Longgang district.

Qin Qianhong, a law professor at Wuhan University, said on Thursday the cases show the complexity of police gun control as weapons are necessary for police to control riots or protect themselves.

"At least two police officers should be on spot when a gun will be used, to supervise the use, especially as some police officers are too impulsive," he said.

To avoid possible harm the gun may cause members of the public, China should learn from practices of other countries, such as limiting the number of bullets or using alternatives such as rubber bullets or pepper spray, he said.

When police are not on duty, they should not carry their guns and a strict system of supervision should be put in place, Qin added.

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