Police have clashed with striking subway workers in Sao Paulo as traffic chaos grips the Brazilian mega-city less than a week before it hosts the World Cup's opening game.
Police fired tear gas and swung batons to beat back the picketing strikers on Friday after commuters tried to enter a major metro station amid torrential rain that has added to the traffic misery.
The indefinite work stoppage, now in its second day, has raised fears of unrest when the country's business hub hosts next Thursday's game between Brazil and Croatia.
The clashes came as Brazil's national team prepared to play their last friendly on Friday night against Serbia in Sao Paulo's Morumbi stadium, not the new Corinthians Arena, which has yet to be finished six days from the inaugural match.
The Sao Paulo metro is the main link to the Corinthians Arena, and the strike could force organisers to come up with last-minute alternative transportation for tens of thousands of fans.
The traffic mayhem has stranded the 4.5 million passengers who use the subway system daily in the sprawling city, while bumper-to-bumper traffic stretched for up to 250km.
Another strike by 75 per cent of Sao Paulo's traffic police exacerbated transport problems.
The chaos in Sao Paulo is the sort of incident that Brazilian and world football body FIFA want to avoid following the violent protests that marred last year's Confederations Cup, a World Cup dress rehearsal.
It was in this city of 20 million people that mass protests erupted a year ago as citizens took to the streets to voice anger at rising public transport fares.
The unrest ballooned into nationwide demonstrations against the more than $US11 billion ($A12 billion) being spent on the World Cup.
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