Jakarta, Indonesia (CNN) -- A volcano that had been inactive for more than 400 years erupted in Indonesia early Sunday, causing thousands of people to flee their homes, officials said.

Mount Sinabung in North Sumatra province had been inactive since the 1600s, but spewed volcanic ash nearly a mile into the air Sunday, said Surono, head of the country's volcanology and geology agency.

"We don't know the character of this volcano because it's been dormant for so long," he said.

There were no reports of casualties or injuries.

"The situation is under control. Emergency response teams are already on the scene," said Priyadi Kardono of the National Disaster Management Agency.

Officials have evacuated 12,000 residents living in 14 villages near the volcano, which erupted just after 12:15 a.m. Sunday (1:15 p.m. ET Saturday), the official Antara news agency reported.

"We felt strong tremors last night. It was a volcanic quake," Indonesian Red Cross worker Muhammad Isral told the agency. "After that, the crater of Mount Sinabung spewed glowing lava. And trees in the mount slopes were burnt. It was followed by thick clouds that caused visibility to be only about five meters."

On Saturday, the Center for Volcanology and Geological Disaster Mitigation issued a warning and ordered evacuation of a 6 km (3.7 miles) radius around the volcano.

Surano said investigators are monitoring and studying the volcano. Based on the data they have now, he said, a large, destructive eruption is unlikely.

No hazardous gas had been detected after Sunday's eruption, he said.

CNN's Andy Saputra contributed to this report.