An Indonesian volcano that has been dormant for hundreds of years erupted for a second straight day on Monday, forcing thousands of people out of their homes.

Mount Sinabung in North Sumatra has long been considered inactive because it last erupted more than 400 years ago.

It erupted for the first time over the weekend and erupted again early Monday, spewing clouds of soot and ash into the air, the Indonesian meteorology agency said.

(CBC)

As many as 30,000 people who live near the mountain have fled their homes, freelance journalist Michel Maas reported.

Maas said villagers living along the slopes have packed their belongings and headed to emergency shelters, mosques and churches.

"Nobody is sure how long this is going to last," Maas told CBC News in an interview from Indonesia. He said local residents are trying to move livestock to safety because they are not sure how long they will have to stay in emergency shelters.

Health officials have been distributing thousands of face masks to help people protect themselves from the ash and smoke billowing into the air.

While two people have died — a 64-year-old woman from respiratory problems and a 52-year-old man from a heart attack — it was too early to say if the volcano was to blame, said Priyadi Kardono of the National Disaster Management Agency.

Children at a North Sumatra shelter are entertained by a band while Mount Sinabung spews ash and soot. (Beawiharta/Reuters)

Sinabung last erupted in 1600, so observers don't know its eruption pattern and admitted over the weekend that they had not been monitoring it closely before it started rumbling days ago in the lead-up to Sunday's first, less-powerful blast.

"We really have no idea what to expect," Surono, a government volcanologist who uses only one name, said after the mountain's alert was raised to the highest level.

"We don't know what set it off, how long it will continue or whether we should expect … more powerful eruptions."

Indonesia is spread across 17,500 islands and is prone to volcanic eruptions and earthquakes because of its location within the so-called "Ring of Fire" — a series of fault lines stretching from the Western Hemisphere through Japan and Southeast Asia.

With files from The Associated Press