According to the Infobae news portal, the traffic on the main avenue of the Argentine capital was shut down for two hours on Wednesday amid mass actions.
The participants of the demonstrations marched along the city's streets carrying banners with slogans protesting the summit, the International Monetary Fund (IMF) and the administration of Argentine President Mauricio Macri.
Argentine public organizations have also taken part in the demonstrations, with the rally hosted by activist group MOCASE Via Campesina having brought together about 50,000 people at a stadium.
According to media reports, protests against G20 summit are set to continue into Friday.
The G20 summit will be held in Buenos Aires on Friday and Saturday.