Indonesia's Marapi volcano spewed clouds of ash half-a-kilometre high into the sky on Wednesday, the country's volcanology agency said, a week after eruptions killed 23 climbers.

The 2,891-metre-(9,485-foot)-high Marapi, one of Sumatra island's most active volcanoes, erupted at around 6 a.m. local time (2300 GMT) on Wednesday morning and again at noon, Hendra Gunawan, the chief of Indonesia's volcanology agency, said.

The eruption, he added, was relatively minor given recent activity, but the alert for the volcano remained at the second-highest level.

Footage seen by Reuters showed large clouds of grapy ash billowing from Mara pi's crater, and local residents carrying out their daily activities from a safe distance.

Local authorities banned people from climbing the volcano following last week's eruption, the deadliest since 1979 when 60 people were killed.

Indonesia straddles the so-called "Pacific Ring of Fire," an area of high seismic activity that rests atop multiple tectonic plates.

With more than 140 volcanoes, Indonesia has the largest population globally living in close range to a volcano, including 8.6 million people within 10 km (6.2 miles). (Reporting by Ananda Teresia; editing by Mark Heinrich)