The Chaiten volcano in southern Chile has erupted with renewed strength, belching thick clouds of ash and hurling molten rocks into the air, regional authorities said Friday.

The 1,000-meter (3,280-foot) tall Chaiten volcano, located some 1,300 kilometers (800 miles) south of Santiago, first began to erupt in May after lying dormant for centuries.

"There has been an increase in the volcano's activity," Sergio Galilea, the governor Los Lagos region, told reporters Friday.

Galilea said that witnesses reported seeing two new craters, and of seeing "significant gas emanations and volcanic material" coming from the volcano.

The National Service of Geology and Mining said it registered 15 low-level earthquakes early Thursday in the volcano area.

On May 6, at the height of Chaiten's activity, a column of volcanic ash rose 30 kilometers (19 miles) high, grounding flights across a large swathe of Chile and Argentina. Ashes drifted east as far as the Argentine capital of Buenos Aires.

Authorities earlier evacuated the 4,000 residents of the town of Chaiten, located a mere 10 kilometers (six miles) from the volcano.

Since the volcano had calmed down in the past weeks officials were hoping to let evacuees return to recover their belongings -- but that plan was put on hold "until we are certain that this increased activity is something temporary," said Galilea.