Police in Shanghai have cracked a major child trafficking ring following the arrest of 47 suspects and rescue of 21 babies after a months-long crackdown.

The sting operations have been ongoing since last spring and involved police in five Chinese provinces.

The most recent raid netted 18 suspected child traffickers and 12 babies.

China has a thriving black market in babies who are abducted or bought from poor families and sold to couples who are childless or want more children, as well as girls and women who are sold as brides.

Many of the children were kidnapped from south-west China's Yunnan province and taken by train to eastern China's Jiangsu and Shandong provinces. It was unclear if any of the babies were meant to be passed on to families in Shanghai.

Nationwide, police have rescued 2,008 kidnapped children and solved 1,717 cases since the crackdown was launched on April 9, according to a report in the People's Daily.

China's Ministry of Public Security has said it is setting up a DNA database to combat child trafficking.

The database will include DNA from the parents of abducted children and samples from children who are suspected of having been abducted or vagrant children with an unclear history.