A volcano in western Indonesia erupted Sunday, belching a column of ash around three kilometers into the sky and forcing the evacuation of dozens of hikers, officials said.

Mount Marapi on the island of Sumatra, with a peak of 2,891 meters, is on the third-highest alert level of Indonesia's four-step system and authorities imposed an exclusion zone around its crater.

There were no immediate reports of damage or casualties after the eruption at 2:54 pm local time (0754 GMT), but earlier in the afternoon officials said several dozen hikers were "unaccounted for".

One of those still coming down the mountain was 19-year-old student Zhafirah Zahrim Febrina, whose mother Rani Radelani shared a video of her daughter who is seen covered in ash and appealing for help.

"She WhatsApped. She said she didn't have any strength. She was hiking since Friday," her mother told AFP.

"She is coming down along with her friends."

Rescue teams have been deployed to help bring mountaineers down to safety, the West Sumatra Natural Resources conservation agency said.

"The… agency team are conducting evacuations. Hopefully, there are no fatalities and everyone is safe," Dian Indriati, the interim head of the agency said in a video statement.

It said 70 hikers had checked in since Saturday via an online booking system, with 42 accounted for as of 5 pm local time (1000 GMT).

However, the local disaster agency later said 47 hikers had been on the mountain, with 28 still to be evacuated.

Casualty figures in Indonesia can often fluctuate due to miscounting.

Some hikers also may not notify authorities about their presence when entering or leaving such areas, so the true number of unaccounted hikers remains unclear.

Raining ash

Hendra Gunawan, head of Indonesia's Centre of Volcanology and Geological Hazard Mitigation, in a statement, said ash was observed 3,000 meters (9,842 feet) above Marapi's peak.

"Eruptions are still ongoing based on PVMBG instrumental observation," Gunawan said in a statement.

Communities around the Marapi volcano and tourists have been stopped from hiking the Marapi volcano within a three-kilometer radius of its crater.

Ahmad Rifandi, an official at the Mount Marapi monitoring station, told AFP that ash rain was observed after the eruption.

"It has reached Bukittinggi city," he said, referring to the third-largest city in West Sumatra that has a population of more than 100,000.

Local disaster agency official Ade Setiawan said in a statement residents in local villages were "given masks and reminded to stay inside their houses".

Mount Marapi, which means 'Mountain of Fire', is the most active volcano on Sumatra island.

The Indonesian archipelago sits on the Pacific Ring of Fire, where the meeting of continental plates causes high volcanic and seismic activity.

The Southeast Asian country has nearly 130 active volcanoes.