By Rosalba O'Brien and Anthony Esposito
SANTIAGO (Reuters) - An ash cloud from the Calbuco volcano in southern Chile that erupted unexpectedly on Wednesday was blowing into Chile and Argentina on Thursday, forcing the cancellation of flights from nearby cities in both countries and blanketing residents in ash.
The volcano, which last had a major eruption in 1961, has belched a spectacular plume of ash and smoke around 15 kilometres into the sky near the popular tourist town of Puerto Varas, some 1,000 kilometres (625 miles) south of Santiago.
Winds have already carried part of the ash cloud to the city of Chillan, some 400 kilometres south of Santiago, and could reach the capital by the end of the day, said government meteorologist Arnoldo Zuniga.
Most of the ash, however, was headed over the Andes mountains into neighbouring Argentina.
"We don't rule out that the cloud could reach part of Buenos Aires over the next 48 to 72 hours," said Zuniga.
Volcanic ash can damage aircraft and makes flying dangerous. In 2011, the eruption of Chile's Puyehue volcano sent ash high into the atmosphere, leading to flight cancellations as far away as Australia.
International travel was unaffected as of Thursday afternoon, but LATAM Airlines Group SA's (SN:LAN) Chilean arm, LAN, has cancelled over 20 domestic flights to and from the affected region since Wednesday. Local carrier SKY Airline has also cancelled flights to and from the city of Puerto Montt.
In Argentina, Bariloche and Neuquen airports were shut. Flights by LAN Argentina, state-owned Aerolineas Argentinas and Lade, owned by the Argentine Air Force, were affected.
Calbuco erupted twice over the last 24 hours and has now paused, but it remains unstable and could erupt again, experts said.
Over 4,000 people have been evacuated from the immediate area, authorities said, with the emergency services focusing on the small town of Ensenada, some 15 kilometres from the volcano. TV pictures showed a thick layer of gray ash coating nearby towns.
No one has been reported killed, and a climber who was close to the summit when the eruption occurred and reported missing, has been found alive and in good health.