At least 34 people were confirmed dead and more than 200 injured but authorities were still collecting information from devastated areas.

"The latest information we have is that 26 people are dead... in Mamuju city," said Ali Rahman, head of the local disaster mitigation agency, adding "that number could grow".

"Many of the dead are buried under rubble," he said.

Separately, the national disaster agency said at least eight people had died in an area south of Mamuju, a city of some 110,000 in West Sulawesi province, bringing the total death toll to 34.

The magnitude 6.2 quake early Friday was centred 36 kilometres (22 miles) south of West Sulawesi province’s Mamuju district, at a depth of 18 kilometres (11 miles), the US Geological Survey said.

Strong aftershocks could follow a 6.2 magnitude earthquake that struck Indonesia's Sulawesi island early on Friday, the chief of Indonesia's Meteorology and Geophysics Agency (BMKG) said. 

Dwikorita Karnawati told a news conference there had been at least 26 aftershocks after two strong quakes had rocked the area since Thursday afternoon.

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Several buildings in Majene were severely damaged, including 62 homes, a health unit centre and a military office.

The strong quake also caused power and phone service outages and landslides along roads.

A hospital in Mamuju, a city of some 110,000 in West Sulawesi province, was levelled.

"The hospital is flattened, it collapsed," said Arianto from the rescue agency in Mamuju city, who goes by one name.

"There are patients and hospital employees trapped under the rubble and we're now trying to reach them," he added, without giving a specific figure.

Death toll could rise

Rescuers were also trying to reach a family of eight trapped under the rubble of their destroyed home, he added.

The country's search-and-rescue agency earlier said at least one hotel had collapsed after the quake struck at 2:18 am local time Friday (1818 GMT Thursday).

It later clarified that the hotel had partially caved in, while the regional governor's office also suffered extensive damage.

A Mamuju resident said damage across the city was severe, but the full extent of the disaster and casualties was not immediately clear.

"Roads are cracked and many buildings collapsed," said 28-year-old Hendra, who also goes by one name.

"The quake was very strong... I woke up and ran away with my wife."

National Disaster Mitigation Agency spokesman Raditya Jati said three people had been killed and 24 injured.

The death toll could rise.

In a video released by the National Disaster Mitigation Agency, a girl trapped in the wreckage of a house cried out for help and said her mother was alive but unable to move out. "Please help me, it's hurt," the girl told rescuers, who replied that they desperately wanted to help her.

In the video, the rescuers said an excavator was needed to save them. Other images in the video showed a severed bridge and damaged and even flattened houses. TV stations reported the earthquake damaged part of a hospital and patients were moved to an emergency tent outside.