The Chilean congress has been evacuated after protesters attempted to force their way into its grounds during a mass demonstration over entrenched inequality in the South American country.

Police fired tear gas and water cannons to fend off angry demonstrators on Friday night after hundreds of thousands of Chilean protesters flooded the city for a peaceful march, in one of the biggest protests yet since violence broke out a week ago over a hike in public transport fares.

Demonstrators waved national flags, blew whistles and horns and held up placards urging political and social change as they walked for miles from around the capital Santiago to converge on Plaza Italia.

Santiago governor Karla Rubilar said almost a million people marched in the capital - more than five percent of the country’s population.

The demonstrations were a sign that economic concessions by president Sebastián Piñera have failed to ease public anger.

His administration announced that it would increase the minimum wage and the lowest state pensions, roll back the subway fare increase and put a 9.2 per cent increase in electricity prices on hold until the end of next year.

But on Friday, hundreds of trucks drove slowly on a main highway that skirts Santiago, where stone-throwing protesters have fought riot police for more than a week. Some Chileans in cars and motorcycles joined the protest, held to demand an end to private highway tolls.

Most car drivers pay between $35 and $130 a month to use highways around Santiago, depending on how much time they spend on the roads. Truckers pay much more because of the long distances that they travel.

Many Chileans earn between $560 and $760 a month, making it hard to pay for basic needs, let alone drive on the highways.

There will be no further highway toll fee increases this year under Chilean law, transport minister Rafael Moreno said.

Operators of some subway lines in Santiago also stopped service, further disrupting a transport network affected by burning and vandalism of stations in some parts of the city.

About 40 per cent of Santiago’s metro was functioning on Friday, though several thousand buses have been deployed in an attempt to make up for the disruption.

Most of the demonstrations over the high cost of medicine, water and other basic needs have been peaceful. But instances of arson, looting and alleged brutality by security forces have shocked many in a nation known for relative stability.

According to Chile’s human rights watchdog, more than 2,000 people have been detained and over 500 injured.

The government has declared a state of emergency and imposed curfews in 12 out of Chile’s 16 regions.

Former Chilean President Michelle Bachelet, now the UN’s top official on human rights, will send a three-member team to Chile to examine allegations of violations.