On Tuesday the government ordered a 9-mile (15 km) exclusion zone around the 10,253-foot (3,125 meter)-high volcano and ordered the evacuation of around 40 people from the area, about 435 miles (700 km) south of the capital Santiago.

"There is renewed activity as lava is flowing towards the Calbuco River," said Juan Cayupi, a volcanologist at the state National Emergency Office. "(The lava) has reached around 800 meters (2,600 feet) to a 1,000 meters (3,300 feet) from the crater."

Cayupi said he flew over the volcano on Thursday and saw gases emanating from a small dome in the interior of the crater, but saw no lava at the time.

"The risk in this case is that there could be abrupt melting of snow because of the lava, which could produce torrents (of water and other material)," he added.

The renewed activity comes after Chaiten volcano, 760 miles (1,220 km) south of Santiago in Chilean Patagonia, started erupting on May 2 for the first time in thousands of years, spewing ash, gas and molten rock.

The nearby town of Chaiten has been caked in volcanic ash and the volcano continues to emit hot gas and ash. Chile's flagship carrier LAN suspended flights to the southern town of Puerto Montt on Tuesday, citing ash from the volcano. Jet engines need thorough servicing after coming into contact with the ash.

A 30-mile (50 km) radius around Chaiten volcano was evacuated, and the area remains off limits to thousands of evacuees.

Ash from Chaiten, which initially soared as high as 20 miles (30 km), as well as rain swelled rivers in the area. Flooding damaged dozens of houses, carrying some wooden homes off their foundations.

Chile's chain of some 2,000 volcanoes is the world's second-largest after Indonesia's. Around 50 to 60 are recorded to have erupted, while a total of 500 are deemed potentially active. (Writing by Simon Gardner; Editing by Eric Beech)