Four former prison guards in northeast China's Heilongjiang Province were handed jail terms from a year and four months to two and a half years on Friday for turning a blind eye to a prisoner who seduced and blackmailed a number of women while behind bars.

The four defendants stood trial at Longjiang County People's Court in the city of Qiqihaer on Friday morning.

Wang Meng received one year and four months and Zhu Dengtao a year and a half for dereliction of duty. Li Haijun and Liu Yandong were sentenced to two and a half years, and a year and eight months for abuse of power, according to the court.

The prisoner, Wang Dong, who has been incarcerated since December 2012 at Nehe Prison, used the cellphone messaging app WeChat to chat with several women who lived near the prison and "established lover relationships with them" during incarceration.

He asked these women to visit him in prison, where he extorted money from them by threatening to spread the videos and pictures that they had sent of themselves naked.

The blackmail came to light when one of Wang Dong's victims reported that she was being blackmailed to the police in late 2014.

Wang Dong was fined 220,000 yuan (33,968 US dollars) and given 13 years and nine months, including the time remaining under his original sentence for kidnapping, by Nehe City People's Court in July.

Wang Meng had been in charge of one unit of the Nehe Prison where Wang Dong was jailed. It was a result of his dereliction of duty that Wang Dong violated prison regulations such as using cellphones.

Zhu Dengtao, deputy director of the unit, allowed Wang Dong to have dinner with three women in prison on separate occasions and even permitted "flirtatious behavior" with one of them. After one dating, Zhu failed to search Wang Dong and he also turned a blind eye to Wang's use of the cellphones.

Li Haijun, a prison guard at the Nehe Prison, helped prisoners bring cellphones into the prison and took liquor for sale as well.

Liu Yandong, head guard, accepted bribes from two women and allowed them to have dinner with Wang Dong in prison, according to the court.

Only Li will lodge an appeal.