Brazil's currency has lost one-third of its value in recent weeks
Latin American investors are braced for more turbulence a day after markets reacted gloomily to government interventions in Argentina and Brazil.
Argentine stocks have sunk 20% since President Cristina Fernandez unveiled plans on Tuesday to nationalise private pension funds.
Brazil's stocks fell 10% despite moves to let state-run banks buy up stakes in private financial institutions.
Trading in Sao Paulo was halted for the fifth time in recent weeks.
Elsewhere in the region, Mexican stocks sank 7%, Chile's index fell 6% and Colombia's dropped 5%.
Correspondents say international demand is declining for many of Latin America's commodity exports, including oil, copper, iron ore and soy as global growth slows amid the current financial global crisis.
The Brazilian currency, the real, has lost one-third of its value against the US dollar in recent weeks.
Brazil hopes its plan, announced on Wednesday, to allow government-controlled Banco do Brasil and Caixa Economica Federal to purchase shares in private financial institutions will eventually succeed in shoring up the market.
The BBC's Gary Duffy, in Sao Paulo, says that while Brazil is better placed to weather the storm than in previous crises, there are increasing signs of unease about the potential fallout for Latin America's biggest economy.
Earlier this week President Luiz Inacio Lula da Silva said for the first time the downturn might eventually force a change in the country's budget.
Meanwhile, Argentine investors also took cover following President Fernandez's plan to take over $30bn (£18bn) in private pension fund assets.
She said the nationalisation would protect retirement funds from the global financial crisis, but analysts said the move would drain company access to private capital.
Argentina's Congress is expected to approve the proposal within weeks.
Despite Latin America's market turmoil, an International Monetary Fund report said on Wednesday the region was expected to cope better than in previous crises, and should see growth of about 3% next year.