Commuters faced major traffic woes in Sao Paulo Thursday as subway workers went on strike, causing chaos in the Brazilian metropolis a week before it hosts the World Cup opener.

The Sao Paulo metro is the main transport link to the economic capital's host stadium, and the indefinite strike could pose a massive logistical headache for organizers -- as well as the 4.5 million passengers who use it daily.

Frustrated commuters broke entrance grilles at the station that serves the stadium, Corinthians Arena, forcing system operators CPTM to take emergency measures to open it.

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

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

Sao Paulo was where mass protests erupted a year ago as citizens took to the streets to voice anger at rising public transportation fares.

The unrest ballooned into nationwide demonstrations against the more than $11 billion being spent on the World Cup.

A million protesters turned out last June during the Confederations Cup, a World Cup dress rehearsal.

The protests turned violent at times, overshadowing the tournament and raising fears of a repeat this year.

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

"I've come in from Sao Bernardo dos Campos (in the suburbs) and now I don't know how I am going to reach my destination," complained an exasperated commuter, 19-year-old Andre Luiz Diaz.

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.

Many say the national mood is much the same as during last year's riots.

"Nothing has changed. The people took to the streets and no level of government has managed to respond to their demands," said Antonio Carlos Costa, founder of activist group Rio da Paz.

"Brazil has the seventh-largest economy in the world, but it ranks 85th on the human development index, there are 50,000 murders a year. It's normal for people to get angry when so much money is being spent building stadiums."

President Dilma Rousseff has defended her government's preparations for the tournament, insisting the money spent would leave a legacy of airports and transportation infrastructure that would 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, to which firefighters have not given safety clearance 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 Tuesday, play Serbia on Friday in a final warm-up before taking on Croatia in the kick-off match.