Commuters faced transport chaos in Sao Paulo on Thursday as subway workers went on strike in the Brazilian economic capital a week before it hosts the opening match of the World Cup.

The Sao Paulo metro is the main link to the city's stadium, and the indefinite strike could pose logistical headache for cup organizers -- as well as the 4.5 million passengers who use the system daily.

Frustrated commuters broke entrance grilles at the station that serves the stadium, Corinthians Arena.

After some of them jumped onto the tracks, system operators CPTM decided to open the station in a bid to calm the situation.

With more people using their cars, bumper-to-bumper traffic stretched for up to 209 kilometers (135 miles) during the morning rush-hour, the worst congestion so far this year and the third worst ever recorded in the sprawling city of 20 million people.

Another strike by 75 percent of Sao Paulo's traffic police exacerbated transport problems.

The subway strike affected three of the city's five metro lines, a system employee told AFP.

Governor Geraldo Alckmin said the state was seeking a court injunction declaring the strike "abusive" and hoped to have a decision by the end of the day.

Sao Paulo was where 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 $11 billion being spent on the World Cup.

During the Confederations Cup, a World Cup dress rehearsal, protests drew a million people into the streets -- at times turning violent, overshadowing the tournament and raising fears of a repeat this year.

Amnesty International said the police response to the protests had been characterized by violence and abuses, and warned Brazil against cracking down on demonstrations during the World Cup.

"Brazil's deficient policing record, reliance on the military to police demonstrations, lack of training and an atmosphere of impunity creates a dangerous cocktail," said Atila Roque, Amnesty's country director for Brazil.

The protest movement has lost momentum since last June, but Thursday's transportation chaos risks rekindling anger with one week to go to the opening ceremony and match.

"The problem is going to be getting home this evening. It's not even worth it to go to work, the train is packed and tonight it's going to be worse. People were fighting to get onto the train," commuter Edith Carvalho, 40, told AFP.

Workers went on strike at midnight after negotiations on a salary increase fell through. They rejected an offer of 8.7 percent, insisting on at least 10 percent, said the president of their union, Altino Melo dos Prazeres.

"If there's money for the Itaquerao (the nickname for Corinthians Arena) and the World Cup, how is it they don't have any money for public transportation?" Prazeres was quoted as saying by newspaper O Estado de Sao Paulo.

He said any offer would have to be in the double digits to keep up with inflation -- a growing concern in Brazil, which is struggling with slowing growth and rising prices.

President Dilma Rousseff has defended her government's preparations for the World Cup, insisting the money spent will leave a legacy of airports and transportation infrastructure that will benefit Brazil for years to come.

But the government has also faced criticism for chronic delays and disorganization.

Workers are still scrambling to finish several of the 12 host stadiums, including Corinthians Arena, which has not received safety clearance from firefighters to operate at full capacity.

Eight workers died in construction accidents at the stadiums, including three in Sao Paulo.

Much of the other promised infrastructure has been shelved, from roadworks and a high-speed train to subway and monorail lines.

Meanwhile, teams continue trickling into Brazil. Chile are due to arrive later Thursday, joining Australia, Croatia and Iran.

Brazil, who routed Panama 4-0 in a friendly on Tuesday, play Serbia on Friday in a final warm-up before taking on Croatia in the opening encounter of the World Cup tournament itself.