JOHANNESBURG — South African construction workers at stadiums being built for the 2010 World Cup have gone on an indefinite strike which could derail next year's tournament.

About 70,000 workers at stadiums across the country downed tools Wednesday after wage negotiations deadlocked earlier this week.

Workers are demanding a 13 percent pay increase while employers are only offering a 10.4 percent rise.

The strike could delay the completion of flagship projects such as the Soccer City stadium in Johannesburg and the Green Point stadium in Cape Town. Contractors are racing to meet a December deadline for building work to be finished.

Thousands of workers protested at the construction sites and police are monitoring the situation.