Eleven hikers were found dead Monday and another 12 were missing after a volcano erupted in Indonesia, with rescuers racing to carry injured and burned survivors down the mountain on foot.

Rescuers worked through the night to find dozens of hikers stranded on Mount Marapi on the island of Sumatra after it spewed an ash tower 3,000 metres (9,340 feet) — taller than the volcano itself — into the sky on Sunday.

The dead hikers were found near Marapi's crater after the 2,891-metre volcano rained ash on nearby villages, according to a local rescue official.

Twelve were missing, three more were found alive and 49 had safely descended from the crater, some with burns and fractures, the official said.

"They are being carried down manually, rescuers are taking turns bringing them down. We can't do an air search with a helicopter because the eruption is ongoing," said local rescue agency chief Abdul Malik, who added about 120 rescuers were involved in the search.

The three other people who had been found alive were yet to be taken down the mountain, along with the 11 dead.

Those three survivors were found near the crater and "their condition was weak, and some had burns," Malik said.

A clip shared with AFP showed a rescue worker with a flashlight strapped to his head piggybacking a hiker, who moans in pain and says "God is greatest" as she is led to safety in the darkness of night.

Zhafirah Zahrim Febrina, one of the rescued hikers, is shown in a video message from the volcano desperately appealing to her mother for help.

The 19-year-old student appeared shocked, her face burnt and her hair matted with thick grey ash.

"Mom, help Ife. This is Ife's situation right now," she said, referring to her nickname.

She is now in a nearby hospital with her father and uncle after being trapped on the mountain on a hiking trip with 18 school friends.

"She is going through a tremendous trauma," said her mother Rani Radelani, 39. 

"She is affected psychologically because she saw her burns, and she also had to endure the pain all night."

'Tremendous trauma'

Local rescue agency spokesperson Jodi Haryawan said the rescue efforts had been broken up by sporadic eruptions but the search was still going despite the risks.

"Once it was safer they continued the search. So the search was not halted," he told AFP.

Rudy Rinaldi, head of the West Sumatra Disaster Mitigation Agency, told AFP some of the rescued hikers had suffered burns.

"Those who are injured were the ones who got closer to the crater," he said.

At least eight people suffered burns, one had burns and a fracture and another had a head wound, according to a list of those found from Basarnas, a national search and rescue agency, seen by AFP.

Ahmad Rifandi, an official at the Mount Marapi monitoring station, told AFP that ash rain was observed after the eruption and had reached Bukittinggi, the third-largest city in West Sumatra that has a population of more than 100,000.

The plume of smoke and ash blocked out the sun after the eruption and coated nearby cars, scooters and ambulances.

Marapi is on the second alert level of Indonesia's four-step system and authorities have imposed a three-kilometre exclusion zone around its crater.

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.

As the search goes on for the missing 12 hikers, Febrina's family was relieved she was one of the lucky ones.

Good news arrived in the form of a livestream on video app TikTok by a member of the rescue services, in which Radelani saw her visibly shaken daughter.

"It felt incredible, praise God she has been found," Radelani said.

"If she asks me to allow her to climb a mountain, I'll say no."