Flights were canceled for several hours in Uruguay and Argentina Tuesday due to volcanic ash from the four-month-long eruption of the Puyehue volcano in Chile, airport authorities said.

Laura Vanoli, Uruguay's chief aeronautic meteorologist, said the country was almost entirely covered by an ash cloud.

"It's remnants of ash," she said, adding that there will be a risk of disruption as long as the volcano remains active.

About a dozen flights by airlines including Aerolineas Argentinas, American, Iberia and TACA were suspended in Uruguay, while other flights were delayed, the website of the Carrasco International Airport serving Montevideo said.

In Buenos Aires, airport authorities said some 20 flights were canceled, and said other flights were delayed because of poor visibility due to the ash.

However by the afternoon air traffic was returning to normal in both Uruguay and Argentina, though with delays due to the postponed flights.

Since the volcano's eruption on June 4, air travel in much of the southern cone of South America, and as far away as Australia, has been periodically disrupted by ash clouds streaming east out of the Chilean Andes.

Chile's National Geology and Mining Service said that ashes from the Puyehue -- which continues belching, though at a lower intensity -- could affect air travel for months.

The decision to delay or cancel flights is taken by the airlines over concern about how the fine ash would affect airplane engines.