Mount Marapi in West Sumatra province erupted at 1:04 pm (0604 GMT), spewing thick grey clouds of ash two kilometres (1.2 miles) above its peak, the national disaster mitigation agency, or BNPB, said in a statement.
The volcano -- one of Indonesia's most active -- has been at the second-highest alert level of the country's four-tiered system for weeks, with authorities advising people to stay outside a 4.5-kilometre exclusion zone around its crater.
Local residents are advised to be vigilant over threats of cold lava flows following the eruption, BNPB spokesman Abdul Muhari said.
"People are urged to stay away from river areas that originate from the Marapi volcano and be on alert to the potential dangers of lahar that could occur, particularly when it rains," he said.
Cold lava, also known in Indonesia as lahar, is a mixture of volcanic materials like ash, sand and pebbles carried down a volcano's slopes by rain.
Heavy rains this month caused volcanic debris to flow into districts near Marapi, killing more than 60 people, destroying dozens of houses, and damaging roads and mosques.
In the event of ash falls, residents should wear face masks to prevent respiratory problems and clear volcanic ash from the roofs of their houses to prevent collapses, geological agency head Muhammad Wafid said in a statement on Thursday.
Indonesia, a vast archipelago nation, experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire".
In December, Marapi erupted and spewed an ash tower 3,000 metres (9,843 feet) into the sky.
At least 24 climbers, most of them university students, died in the eruption.
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