WORKERS on Sao Paulo's metro have started an indefinite strike, disrupting three of the city's five subway lines and stranding millions of commuters a week before the World Cup kicks off.

Train, bus and police strikes have been common in Brazil as workers use the high profile event as an excuse to push for higher salaries and benefits, walking off the job regardless of whether courts grant the strikes legal status.

Frustrated passengers yesterday broke the doors to a stalled train and walked onto the tracks at the Itaquera stop when their commutes were interrupted. The station, which will transport thousands of soccer fans to the Corinthians arena for the World Cup's opening match on June 12, was operating normally by mid-morning.

More than four million commuters were left without transportation. Traffic was more congested than usual in Brazil's business hub although less severe than it was a week ago when a two-day bus strike caught the city by surprise.

Many football fans are expected to rely on limited public transportation to get to stadiums on game days at 12 host cities during the month-long tournament.

Broken promises over new public transport projects contributed to waves of street protests last year and have hurt the popularity of President Dilma Rousseff ahead of elections in October.