China's capital has issued 530,364 identification cards to migrant workers to make sure they get paid, local media said. China has an estimated 200 million migrant workers who in recent years have flocked from the vast, poor countryside to the booming cities. Rights groups say they often lack health care, have their pay withheld and are vulnerable to exploitation.

Amnesty International criticised the government in a report earlier this year for doing too little to protect migrant workers from widespread and institutionalised discrimination. Instead of paying cash, companies wire salaries to the migrant workers' cards, which are connected to a system monitored by the government. The ID cards are similar to bank cards.

"Compared to the previous method of paying workers in cash, using the identification card can assure migrant workers are paid and avoid infringement of migrant workers' rights," the Beijing News said.

The program was launched in April and is open to all migrant construction workers in Beijing. More than 570,000 had signed up so far.