An excavator works on a river affected by ashes from Calbuco Volcano in El Tepu town on May 2. Chilean volcano Calbuco erupted for the third time in eight days on April 29, sending a new cloud of ash and gas high into the sky, although officials said the latest eruption was less powerful than those of last week. [REUTERS / CARLOS GUTIERREZ]

Chilean volcano Calbuco erupted for the third time in eight days on April 29, sending a new cloud of ash and gas high into the sky, although officials said the latest eruption was less powerful than those of last week.

Calbuco spewed more than 200 million tons of ash last week, coating nearby towns, wrecking parts of the salmon industry and forcing the cancellation of flights as far as Buenos Aires 1,400 km away.

The volcano has been quiet this week, but geological officials had warned it was still unstable and could erupt again. The new eruption began at 1:09 pm (1609 GMT), the government's geology service Sernageomin said.

Calbuco, one of the most active along a chain of around 2,000 in Chile, is in the scenic Los Lagos region, a popular tourist destination around 1,000 km south of the capital, Santiago.

TV pictures showed a thick, grey plume spreading quickly into the sky on April 29 afternoon. It was heading south-east over the Andes intoArgentina, said government meteorologist Arnaldo Zuniga.

LATAM Airlines' Chilean arm LAN, which cancelled some flights last week as a precaution because of the ash cloud, said flights in Chile andArgentina were unaffected so far.

A 20-km exclusion zone has remained in place around the volcano since the first sudden eruption on April 22, but some residents have been making short visits to their homes to begin clearing away thick layers of ash and debris.

About 1,500 more people had been evacuated on April 29, interior minister Mahmud Aleuy said. He said there were indications that the eruption was not as powerful as those of last week, when ash and gas reached 17 km into the atmosphere.

"This emission is notably weaker than the previous ones. We are talking about a column of ash no higher than four kilometers," said Aleuy.

Officials said, however, that heavy rain or snow on Friday could lead to complications such as lahares - destructive flows of debris that can wipe out anything in their path.

"This emission should begin to weaken in the coming hours...but we are in an eruptive process, on red alert, and the situation can change at any time," said Sernageomin head Rodrigo Alvarez.