Police have arrested the mother of the 12-year-old boy who was found wandering alone in accident & emergency at Kwong Wah Hospital on July 21.

The 37-year-old woman had returned to the mainland after allegedly leaving her son in Hong Kong. Officers later got in touch with the mother, who said she was a tourist, and expressed a willingness to return to collect him.

The boy was subsequently placed in the Tuen Mun Children and Juvenile Home, while police applied to the Juvenile Court for a care or protection order for the boy.

It's understood he was born in the SAR and holds a Hong Kong ID card.

The mother was arrested on her return to the SAR on Saturday night. She's been charged with child abuse and neglect.

Her case will be heard at the Kowloon City Courts on Monday.