PUCON, Chile (AP) — One of South America's most active volcanoes erupted early Tuesday in southern Chile, spewing heavy smoke into the air as lava surged down its slopes, prompting authorities to evacuate thousands of people.

The Villarrica volcano erupted around 3 a.m. local time, according to the National Emergency Office, which issued a red alert and ordered evacuations. Local media showed images of the volcano bursting at the top, glowing in the dark amid heavy smoke and rivers of lava. Authorities worried that mudslides caused by melting snow could endanger nearby communities.

The 9,000 foot (2,847-meter) volcano in Chile's central valley, 400 miles (670 kilometers) south of Santiago, sits above the small city of Pucon, which has a population of about 22,000 people.

"It was the most amazing thing I've ever seen," 29-year-old Australian tourist Travis Armstrong said in a telephone interview from Pucon. "I've never seen a volcano erupt and it was spewing lava and ash hundreds of meters into the air. Lightning was striking down at the volcano from the ash cloud that formed from the eruption."

Chilean authorities had issued an orange alert on Monday because of increased activity at the volcano. About 3,500 people have been evacuated so far, including tourists, said Interior and Security Minister Rodrigo Penailillo.

Penailillo warned that the eruption was causing numerous rivers in the area to rise as snow along the sides of the volcano began melting. Villarrica is covered by a glacier cap covering some 40 square kilometers (15 square miles) and snow from about 1,500 meters (about 5,000 feet) on up.

Authorities were keeping an eye on four nearby communities that could be endangered by mudslides as the snow melts.

Jose Manuel Reyes, the 37-year-old manager of La Bicicleta hostal in downtown Pucon, said visitors from France, Canada, Australian, South Africa and Brazil watched the early morning eruption from the building's terrace.

"We're still a bit nervous because we don't know what's happening," said Reyes. "There was nervousness, but we haven't seen any panic."

Tourists flock to the area around Villarrica for outdoor activities like kayaking, horseback riding, fishing and hiking around the volcano, which last had a major eruption in 1984. Dozens of tourists were among those evacuated.

President Michelle Bachelet announced that she will travel to areas near the volcano later Tuesday to check on safety preparations and asked residents to remain calm.

The Villarrica has a crater of about 200 meters (yards) in diameter and a lake of lava about 150 meters (yards) deep. It has periodic eruptions every 10 or 15 years.

Chile has more than 2,000 volcanoes in the Andes cordillera and about 90 of them remain active. Villarrica is considered among the country's most dangerous.

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Vergara reported from Santiago, Chile. AP writer Luis Andres Henao also contributed from Santiago.