A couple alleged to have abducted a 13-year-old girl to raise as a future bride for their 22-year-old son have been detained by police.

They took the daughter of a neighbor in Shanghai and then left the city, said officers.

The husband, surnamed Zhang, said they wanted the girl to become their daughter-in-law.

The couple said they had no idea that their behavior had broken the law, police said.

Their son is an alleged accomplice and has been bailed.

The victim, from Hangtou Town in the Pudong New Area, went missing on June 10 after going out to play, said her mother, surnamed Yang, who alerted police.

Officers learned that Zhou and his wife, surnamed Wang, who carried bricks in construction sites for a living, had previously said that they wanted Yang's daughter to marry their son.

Police went to the family's home but discovered they had recently left in a hurry, without even locking the door.

Two days later, to Yang's surprise and relief, her daughter appeared safe and well at her home, throwing herself into her mother's arms.

Wang was later found at her home and taken for questioning by police. Zhou and the son were detained in the days that followed.

Police said the couple are repentant, claiming they just wanted their son to meet the girl and get along well with her.

They hoped they would marry in future.

The couple said they had been worried about their son, as he was shy and seldom had girlfriends.

After they learned that Yang had called the police, they took the girl back to Shanghai, police said.

The pair said they did not know the girl was only 13.