Police clashed with striking subway workers in Sao Paulo on Friday while 3,000 people protested government policies, causing traffic chaos six days before Brazil's mega-city hosts the first World Cup game.

The separate demonstrations raised fears of more unrest when Brazil and Croatia play the first game in the business hub of 20 million people next Thursday.

Police fired tear gas and swung batons to beat back the picketing strikers after commuters tried to enter a major metro station, with torrential rain adding to the traffic misery.

Across town, police officers at the scene estimated that 3,000 people demonstrated peacefully in front of the Central Bank in a protest organized by the Force Union, blocking the street before dispersing.

The protests came as Brazil's national team prepared to play their last friendly Friday night against Serbia in Sao Paulo's Morumbi stadium.

But the first World Cup game will be played in the city's new Corinthians Arena, which has yet to receive safety clearance to operate at full capacity, highlighting Brazil's struggle to be ready for the World Cup.

Officials are hard-pressed to resolve the metro strike because the subway will be the main link to the arena for legions of fans.

Workers went on strike early Thursday after negotiations on a salary increase fell through. They rejected an offer of 8.7 percent, insisting on at least 10 percent.

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 250 kilometers (155 miles).

"I'm going to have to return home. I can't get to work like this. The metro is not going there and with this traffic, it's impossible to go by bus," said Pedro Henrique Rodrigues, a 28-year-old pastry factory worker who stood in a massive line of people waiting for buses.

It was the latest strike to hit Brazil, where bus drivers, teachers and police have staged walk-outs in other cities in recent months to demand better wages.

The chaos in Sao Paulo is the sort of incident that Brazilian officials 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 Sao Paulo that mass protests erupted exactly 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, with more than one million people taking to the streets to demand money for hospitals and schools.

The protest movement has lost momentum since last June, but the transportation chaos risks rekindling anger in the countdown to the opening ceremony.

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

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

Eight workers died in construction accidents at the stadiums, including three in Sao Paulo. Several of the 12 stadiums have yet to be finished.

Rousseff's popularity has taken a hit, with an opinion poll Friday showing that her support for October elections dropped to 34 percent in June from 37 percent in April.

She still led the pack of candidates, however, with her main rival, social democrat Aecio Neves, falling by one point to 19 percent.

Despite Sao Paulo's latest troubles. FIFA president Sepp Blatter predicted on Thursday that tensions would subside once the football began.

"We at FIFA, we are confident, it will be a celebration," Blatter said. "I'm an optimist. After the tournament kicks off I think there will be a better mood," he said.

FIFA secretary general Jerome Valcke acknowledged that organizers faced challenges but that they were "in control" and had "nothing to fear in the coming days."

Meanwhile, teams continue trickling into Brazil. The Dutch team walked along Rio's Ipanema beach after arriving Friday.

Italy, Bosnia and Ivory Coast also landed Friday, joining Chile, Australia, Croatia and Iran.