The principal airports of Argentina and Uruguay are closed and rivers are about to overflow in Chile due to a volcano that began erupting nearly a week ago.
In the southern Argentine resort city of San Carlos de Bariloche, workers have filled 600 dump trucks with ash that had fallen on the main runway.
Buenos Aires authorities say they hope the capital's main airports will be open by Friday evening, when the ash cloud is expected to drift away from the city. The ash can damage airplane engines.
The ash dusted streets in the Uruguayan capital of Montevideo as well as Argentina's Buenos Aires, roughly 850 miles northeast of the Cordon Caulle volcano that began erupting through a gash in the earth on Saturday.
Volcanic ash can damage airline engines, so many flights were canceled between the capitals of Argentina, Chile, Uruguay, Paraguay and Brazil.
Even Argentine President Cristina Fernandez was forced to use a car rather than a helicopter to get to work on Thursday. Her planned meeting with Uruguayan leader Jose Mujica was scrapped because he was unable to fly to Buenos Aires. A meeting in Argentina of South American central bankers and economy ministers also was called off.
Argentina's transport ministry said regional airports serving at least 12 cities closer to the volcano will remain closed until Tuesday or later, due to safety concerns.
About 4,000 evacuees from Chilean towns and farms near the volcano were kept away from home Thursday as gas and ash continued to spew from a wide fissure along the a ridge between two volcanic peaks. Steady rains mixed with the ash and snow to create a slippery mess, spoiling water sources for some 9,000 cows and sheep and threatening to cause flooding along rivers coursing down from snowy mountaintops. Usually frigid river water was measured at a steamy 113 degrees Fahrenheit in places.
Aerolineas Argentinas, Austral and LAN airlines canceled nearly all their international and domestic flights in or out of Argentina on Thursday, and other leading international carriers were cancelling or rerouting flights on a case-by-case basis. Flights to and from Buenos Aires on United Airlines, Iberia, Lufthansa, Delta, British Airways, Avianca and TACA were canceled; one flight on American Airlines was rerouted; the international airport's web site didn't say where.
At least two-dozen flights from six Brazilian cities to Chile, Argentina and Uruguay also were canceled. Airport chiefs in Santiago and Asuncion said similar flights from Chile and Paraguay also were grounded.
The ash plume seems to be "nailed down" over the Argentine capital with prevailing northerly winds dying down, Transportation Secretary Juan Pablo Schiavi said. Argentina's national weather service said the ash is mostly floating at an altitude of more than 19,000 feet, in the path of long-distance flights.
Associated Press Writers Federico Quilodran in Chile, Raul Garces in Uruguay, Pedro Servin in Paraguay and Marco Sibaja in Brazil contributed to this story.