Police in Brazil's biggest city Sao Paulo have used batons and fired tear gas to break the subway strikes by the protesting workers and commuters that have caused chaos in the country's economic capital, according to reports.

The second straight day of commuting chaos on Friday confronted Brazil less than a week before it hosts the opening match of the football World Cup.

"Ana Rosa station, one of the most central stations, was closed and numerous users tried to enter. Clashes broke out between picketing strikers and users and the police had to intervene with tear gas," a military police spokesman told AFP news agency.

More than 200km of traffic choked city streets.

The strike already set a record on Thursday for morning gridlock in Sao Paulo this year and snagged several FIFA officials in over two hours of traffic as they arrived for a conference ahead of the World Cup.

The Sao Paulo metro is the main link to the city's World Cup host stadium, and the strike could force organisers to come up with last-minute alternative transportation for tens of thousands of fans.

It has also stranded the 4.5 million passengers who use the subway system daily in the sprawling city of 20 million people.

Widespread protests

World Cup organisers have urged football fans to use public transportation to stadiums on game days at 12 host cities, but just a fraction of the transportation projects promised for the tournament have been delivered.

Frustration with those broken promises and the ballooning cost of new World Cup stadiums contributed to widespread protests that drew over a million Brazilians into the streets during a warm-up tournament last year.

The government is braced for another wave of demonstrations, but protests so far this year have lacked the spontaneous energy and scale of 2013.

RELATED: Brazil's poor stage an alternative World Cup

Instead, the largest demonstrations have been from homeless groups and striking workers using the backdrop of the World Cup to press their causes.

Protests directly against the tournament have been marked by flashes of violence between police and "black bloc" protesters, eroding popular support.

A judge is expected to weigh the legality of the metro workers' strike on Monday.