File pic: A 13-year-old boy is said to be behind a gruesome beheading video that was circulating on closed Wechat group. Getty

A 13-year-old boy has been arrested after allegedly filming himself killing, then decapitating his mother in southwest China.

Reports from China say that the boy shared the gruesome video of the horrific killing with schoolfriends in a private instant messaging group on popular social media app Wechat.

It was reported that the boy was arrested several days after killing his mother, when a friend showed the clip to his parents in Wenxing, Dazhu county, Sichuan Province on 3 December.

The boy killed his mother after they argued on Sunday (3 December) night, reported Radio Free Asia. Citing local sources they said he was annoyed at his mother for "not giving him money".

The boy allegedly repeatedly demanded 400 yuan (£45) from his mother before the row ensued, local reports said.

After slaughtering her, the boy then threw his mother's head into a toilet bucket and slept with her body still in the same house. It is alleged that he then disposed of her head in a drain near their home the next day.

The boy then went to school, reported Beijing News, but the murder did not come to light until Wednesday (6 December), when one of the boy's classmates showed the clip to a parent.

Radio Free Asia reported that this parent was a friend of the dead woman and she then immediately passed the video onto police. The 13-year-old boy, Yuan Dongzhi, was later arrested by policemen in his classroom when they went into Wenxing Secondary School.

It was reported that the boy was an only child and that police are still investigating the circumstances of the alleged murder.

In a nation where media is tightly controlled, local law enforcement have confirmed that a killing had taken place, but gave no further details.