Tens of thousands of South Korean workers have held a rally to protest against plans to change the country's labour laws.

The Federation of Korean Trade Unions (FKTU) said more than 150,000 members attended the demonstration in the capital, Seoul, on Saturday, while police estimated the crowd at 60,000 people.

The government has said it will begin enforcing laws next year to prohibit companies from paying wages to full-time union representatives and to allow multiple unions for each workplace.

"We, the Federation of Korean Trade Unions, are here to defend the labour unions and labour movement in this land," said Kang Choong-ho, a spokesman for FKTU.

"We will thwart the government's policy by mobilising every means possible. If necessary, we will stage a general strike," Kang said.

Kang also accused the government of Lee Myung-bak, the president, of trying to weaken labour unions.

Riot police were deployed, but there were no clashes and the protesters later peacefully dispersed.

The labour laws' implementation has been delayed for more than a decade because of opposition from labour organisations.

South Korea's two biggest trade unions have joined forces to protest against the laws, which opponents say will undermine workers' rights.