Protesters angry at proposed pension and welfare reforms attacked police close to the National Congress this afternoon, the second protest in a week to turn violent.
Activists lobbed stones, bottles and firecrackers at police as large crowds demonstrated against pension reforms proposed by the government of President Mauricio Macri.
The crowd tried to rip down metal barriers that police had erected to prevent them getting too close to the square beside congress, after similar protests last week descended into violence.
The massed ranks of police officers remained behind their shields without advancing on the demonstrators. Last week, they used water cannon, tear gas and rubber bullets against rock-throwing protesters who burned barricades made of trash near Congress.
The three main trade unions and the opposition had called for a general strike and protests on Monday in the capital to resist the passage of the pension reform bill.
It was the second time the administration has tried to push through the bill. Last Thursday's session had to be cut short as clashes outside escalated, leaving a number of demonstrators injured or under arrest.
A judge then issued a ban on police using firearms against protesters and also forbade undercover police officers from infiltrating the marchers.
Tens of thousands of protesters carrying giant placards and flags tried to converge on the Congress building, occupying 10 blocks of Avenida de Mayo, the street that links Congress to the president's offices at the Casa Rosada.
Macri has been trying to change pension pay-outs in order to lower the country's deficit, which is estimated at five percent of GDP. His aim is to create 2018 savings of 100 billion pesos (US$5.6 billion), equivalent to around a fifth of the deficit.
Unions and the opposition are against imposing the cuts on the poorest sectors of society.
"The bonus payment is a joke," said Juan Carlos Schmid, a leader of the CGT. The measure "is illegitimate and will cause a waterfall of lawsuits against it."
"We have no-one to defend us," said 70-year-old Cristina Sanmero, who found herself caught in the clashes.
"At my age, I have to come here and defend my contributions of 30 years. We're governed by inept people who think that it's easier to take away from the old."