Teargas fired by police at transport workers as mood about hosting tournament remains sour among many

Less than four days before it hosts the opening game of the World Cup, São Paulo became the scene of protests, street fires and teargas on Monday as striking subway workers brought chaos to the city.

The strike – which disrupted half the metro stations and worsened traffic in South America's most populous city – was the latest headache for organisers as national teams from the United States, Spain and Argentina flew in for the start of the tournament on Thursday.

Security is also a major concern, particularly in Rio de Janeiro – the base of the England team – following a recent flare-up of unrest in the city's favelas. Players from Roy Hodgson's England squad were due to visit Roçinha, the nearest shanty town to their hotel, on Monday night as part of an outreach programme.

On Monday night the subway workers' unions announced the strike was being suspended for two days, with a vote to be held to decide whether it would resume on Thursday, when the tournament's first match is due to be played in São Paulo.

Excitement about the tournament is steadily building among the Brazilian public – evident in the growing number of flags in windows and bunting on the streets – but many Brazilians are still uneasy about the $11bn (£6.5bn) costs of hosting the tournament and associate the World Cup with corruption, inefficiency, evictions and misplaced priorities.

Opponents have launched anti-Fifa campaigns on social networks, trade unions have organised strikes and activists have mounted protests in city centres and close to the 12 World Cup stadiums – several of which are still the focus of frantic last-minute construction work.

Although the demonstrations are far smaller than last June's protests of more than a million people, they continue to rattle the government.

The Brazilian president, Dilma Rousseff, who faces re-election in October, has declared security to be a priority, suggesting unnamed forces are conspiring against her.

"Today, there is a systematic campaign against the World Cup – or rather, it is not against the World Cup but rather a systematic campaign against us," the president said during a speech in the host city of Porto Alegre at the weekend.

Trade union leaders feel the imminent start of the tournament will strengthen their hand against a government that will not want to be embarrassed by disruptions when the eyes of the world are on the country.

Subway workers in São Paulo on Monday went into the fifth day of a strike for a 12% wage increase. Station closures forced commuters on to the road and led to 125 miles of traffic jams last week – the worst congestion of the year.

Anti-World Cup graffiti on a building near São Paulo's Arena Corinthians, which was marched on by about 10,000 activists. Photograph: Mario Tama/Getty

Their protest was being supported by activists from the Landless Workers' Movement, who blocked roads and occupied a station in the centre of the city until they were dispersed by riot police using percussion grenades.

The union president, Altino Melo dos Prazeres, said the tough response from the authorities could lead to a further escalation. "If the beating continues we are going to talk to all the sectors. If our people bleed we are going to ask for help from the metalworkers, from the bank workers, and have a day of general strike at the opening of the cup," he said.

The industrial action followed a march last week by about 10,000 activists on the Arena Corinthians, which will host the opening match between Brazil and Croatia. Earlier in the month indigenous protesters in the capital, Brasilia, fired arrows at police during a standoff over land rights.

The Brazilian team has also come under pressure. Last month their bus was attacked by demonstrators; last week the team was booed by sections of the crowd during a drab warm-up game against Serbia.

The government insists it will be able to maintain security during the event. Almost 100,000 police and 57,000 troops will be deployed to protect stadium perimeters, team hotels and training areas, in addition to the private security inside the grounds.

With 500,000 foreign fans now starting to arrive, another challenge will be to countering street crime Police in Rio are several years into a long-term pacification programme to reassert control over favelas that were long the domain of armed gangsters, but the policy has shown signs of unravelling in recent months following several high-profile cases of police brutality.

Last year thousands of residents from Rocinha took to the streets to protest about the disappearance of Amarildo de Souza, a bricklayer who was last seen at police headquarters being interrogated with electric shocks and asphyxiation.

Ten officers were subsequently arrested, but this case – and several others since then – have added to a sense of anger among many favela residents about the brutal actions of police in trying to "pacify" their communities in time for the World Cup.

• This article was amended on 10 June 2014 to correct the spelling of Rocinha.