A 7-year-old boy in Guangzhou whose hand was severed in an unprovoked attack on Wednesday morning has undergone nine hours of surgery to have it reattached.

The attack took place at about 7:30 am on Qiaonanxin Street in Guangzhou's Haizhu district as the boy was walking to school with his mother.

By noon, the police had detained two men on suspicion of carrying out the attack and had also recovered the boy's severed hand.

Initial investigations indicate that the suspects, both from Tianmen in Central China's Hubei province, attacked the boy because of a dispute with his family over a debt.

Surgery to reattach the hand commenced six hours after amputation at Guangdong No 2 General Hospital and was complete by 10:40 pm. However, surgeons said the boy might never recover full functionality in the reattached hand.

Qi Jian, a surgeon from No 1 Hospital Affiliated to Sun Yat-sen University, said severed tendons take between three and six months to recover, while nerves need even longer.

"Severed hands can usually be reattached successfully if surgery take place within 12 hours, unless the hand has been very badly damaged," he said, adding that a patient's recovery depends on many factors.