Brazil's biggest protests in two decades intensified on Thursday as 300,000 people took to the streets of Rio de Janeiro and hundreds of thousands more flooded other cities. The demonstrations came despite the government's U-turn over public transport fare hikes which sparked the protests over a week ago.

Authorities in Rio de Janeiro increased police manpower more than tenfold to deal with the protests.

In the centre of the city, shops pulled down shutters as crowds gathered next to the cathedral, hundreds wearing plastic masks.

But the atmosphere was festive, with music and chanting from the mostly young, middle-class crowd. The wide variety of banners showed how this movement has been a magnet for frustrations that have simmered for many years: "Stop corruption. Change Brazil", "Come to the street. It's the only place we don't pay taxes", "Government failure to understand education will lead to revolution", "We want to change everything wrong in our country", "Stop police violence" – Seemingly the only common theme was a desire for change.

"There are no politicians who speak for us," said Jamaime Schmitt, an engineer. "This is not just about bus fares any more. We pay high taxes and we are a rich country, but we can't see this in our schools, hospitals and roads."

In Sao Paulo protesters carried banners saying "Twenty cents was just the start," referring to the bus fare reductions, as crowds converged along the Avenida Paulista, the broad avenue in the centre of the city.

In the capital, Brasilia, tens of thousands of protesters by early evening marched around the landmark modernist buildings that house Congress, the Supreme Court and presidential offices.

The swelling tide of protests prompted President Dilma Rousseff to cancel a trip next week to Japan, her office said.

In Rio police vastly underestimated the scale of a previous demonstration on Monday, which was largely peaceful but ended with fire and vandalism outside the legislative assembly. Only 150 officers were on duty to deal with a crowd of more than 100,000. Police said they had increased on-duty personnel and placed a battalion of riot police on standby.

The military police spokesman for Rio state, Frederico Caldas, estimated that 8,000 police would be involved in a dual operation to handle the demonstration in the centre of the city and security for the Spanish and Tahitian football teams, who were playing in the Confederations Cup. Police cordoned off the Maracanã stadium, blocking access to protesters during the game. Only ticket-holders were allowed to enter. Inside the stadium, fans sang protest songs and showed support for the throngs of demonstrators gathering in the city.

Police numbers in Rio included 1,200 riot officers who would remain in barracks unless the demonstration turned violent. They were to be armed with teargas and rubber bullets, but the authorities said they would only be used in an emergency.

Thursday's demonstration will be the biggest test of a high-tech police command centre, opened last month, which includes a giant screen with images from hundreds of cameras around the city. For the march on Thursday night, helicopters with high-resolution imaging will also monitor the crowd, but the police denied rumours that drones would be used. "There will be no drones in this operation. That is a false rumourWe don't even have a law that allows drones," said the spokesman.

Early reports seemed to indicate the demonstrations were largely peaceful although police in the northeastern city of Salvador shot tear gas canisters and rubber bullets to disperse a small crowd of protesters trying to break through a police barrier blocking one of the city's streets.

The spark for the unrest was a rise in public transport fares. After early protests were handled brutally by police , the unrest escalated and spread to include a long list of grievances, including corruption, poor public services, and the high cost of stadiums being built for the Confederations Cup and next year's World Cup.