Hundreds of flights out of Argentina and Uruguay have been cancelled as winds blew ash clouds from Chile's erupting Puyehue volcano to the east, dusting large swathes of South American skies.
All flights from Buenos Aires, the Argentine capital, and most out of Montevideo, the Uruguayan capital, were cancelled on Thursday, a spokesperson for Aeropuertos Argentinos 2000, a group that manages the area's airports, told the AFP news agency.
The ash was about 9,000 metres above Buenos Aires, with most flights travelling on average at 10,000 metres, an airport official said.
The Puyehue is located about 1,800km southwest of the Argentinian capital but strong winds have pushed clouds as far east as southern Brazil.
Jose Mujica, the Uruguayan president, was also grounded on Thursday, leaving him to postpone a meeting in Buenos Aires with his Argentine counterpart.
"Humans make plans, but God has the final word," Mujica said on his weekly radio programme. "The ash from the volcano has apparently killed off the trip."
The Puyehue is situated in the Lago Ranco area, about 870km south of Santiago, the Chilean capital, near the border with Argentina.
The volcano began erupting on Saturday for the first time in four decades, and has yet to stop spewing thick clouds of hot ash.
Al Jazeera's Craig Mauro, reporting from Entre Lagos, a town near the volcano, said 25km of roads along the Chilean-Argentinian border were covered in approximately 60,000 cubic square metres of debris, ash and pumice stones.
Mauro said continuing snow at the main crossing near the national park near Entre Lagos is also hindering efforts to clear the border.
Flights in and out of Buenos Aires had been cancelled for much of Tuesday, but resumed on Wednesday.
Volcanic ash "is very dangerous, very abrasive for plane engines and could result in very serious complications," warned Argentine Transportation Secretary Juan Pablo Schiavi.
A crisis committee in Argentina said most air terminals in central and southern Argentina will remain closed "until there is a guarantee that they can operate safely".
Laura Vanoli, director of Uruguay's office of meteorology and aeronautics, told local radio that "the current projection ... is that the cloud of volcanic ash will be with us all day".
Uruguayan authorities also warned that visibility will be "significantly reduced" at least until early Friday.
The last major air traffic crisis in South America was in 2008 when southern Chile's Chaiten volcano erupted, also spreading a thick ash cloud over the region.