Workers at US retail giant Wal-Mart have established their second trade union, state media reported Saturday.

The union was established by 42 employees in the southern city of Shenzhen on Friday, Xinhua news agency said.

The first union was set up six days earlier by 30 employees in the southeast province of Fujian.

Zhou Liang, the Shenzhen union's elected chairman, was quoted as saying that it will "safeguard the lawful rights and interests of the employees" in a bid to harmonize the relationship between the workers and their employer.

A senior Chinese labor union official has vowed to set up union branches in each of Wal-Mart's 60 stores in China, state press reported this week.

For the past two years the world's biggest retailer resisted efforts to establish local unions affiliated to the All-China Federation of Trade Unions (ACFTU), which was set up by the ruling Communist Party and claims some 150 million members.

But Wal-Mart has always maintained its employees were free to set up unions if they wished and insisted it was "in total conformity with Chinese law".

However, joining the union offers staff no guarantee against exploitation, with the ACFTU often criticised by international labor rights groups for favoring business interests over workers' rights.

China's trade union law outlaws workers from forming independent unions or organising collective bargaining activities outside the ACFTU.

Wal-Mart has opened 60 stores in 29 cities and is said to employ more than 30,000 people across the country since it arrived in China in 1996.