GUANGZHOU -- A 16 year old surrendered to police in south China's Guangdong Province on Tuesday evening, hours after two flights were delayed because of a terrorist threat allegedly fabricated.

The suspected hoaxer, surnamed Chen, has been preliminarily diagnosed as mentally ill after surrendering to police accompanied by his father in Zhongshan City, said a spokesman with the city government on Wednesday.

He was mentally unstable at the time of calling the Beijing police emergency line around 6 pm on Tuesday, just a day before he turned 16, according to the spokesman.

Chen's threatening call delayed two Air China flights -- CA4111, from Lhasa to Beijing via Chengdu; and CA1578, from Nanchang to Beijing -- which were due for take off on Tuesday afternoon.

No dangerous items have been found on either of the flights, which took off on Tuesday night after careful rechecks.

Chen was diagnosed as suffering from mental dissociation in a hospital in Zhongshan earlier this year.

According to the willingness of his family, Chen has been sent for medical treatment in Zhongshan on Wednesday evening, added the spokesman.