Oliver Holmes and agencies – At least 97 people have died and more are feared trapped in collapsed buildings after a powerful earthquake struck off Indonesia's Sumatra island at dawn on Wednesday.
Search and rescue teams in Aceh province, an area previously devastated by a massive quake and tsunami on 26 December 2004, used tractors to shift the rubble in attempts to reach people buried in their houses.
The shallow 6.5-magnitude quake hit just north of the small town of Reuleuet, according to the US Geological Survey. There was no tsunami alert.
Major General Tatang Sulaiman, chief of the army in Aceh province, said at least 97 people had died, while four people had been pulled from the rubble alive. Another four or five are known to be buried, but Sulaiman did not say if they are dead or alive.
The rescue effort is concentrated on Meureudu, a severely affected town in Pidie Jaya, the closest district to the epicentre of the undersea quake. Excavators were trying to remove debris from buildings where people were believed buried. Local authorities said there was an urgent need for more excavation equipment and emergency supplies.
President Joko Widodo announced he had instructed his chief of staff to fly immediately to Aceh to monitor the situation.
The quake struck at 5am local time (10pm GMT on Tuesday) as the predominantly Muslim region prepared for morning prayers, local officials said.
Images on television and social media showed cracked roads, collapsed buildings and downed electricity poles. At least five aftershocks were felt in the hours after the initial quake.
"There isn't enough medical staff around," said the Red Crescent's Muklis, who like many Indonesians uses one name, told TVOne.
The national disaster mitigation agency said 273 people were injured, about a quarter of them seriously.
Muhammad Reza Faisal, director of Chik Ditiro general hospital in Pidie Jaya, said the facility, which was damaged by the quake, was overwhelmed with the numbers of injured and many people were being treated in tents pitched on its grounds. He said five of the quake victims died at the hospital.
Hasbi Jaya, a local resident, said his family was asleep when the shaking started. "We immediately ran outside the house but it crumbled. Everything from the roof to the floor collapsed, and was destroyed," he said. "I looked around and all my neighbours' houses were also completely destroyed."
Seismologists said the earthquake was felt across much of Aceh province, which was devastated by the 2004 tsunami.
That quake and tsunami killed more than 170,000 people in Indonesia and tens of thousands more in other countries around the Indian Ocean. Aceh was the worst hit region with more than 120,000 people killed.
The USGS upgraded the magnitude to 6.5 from an initial reading of 6.4 and issued a yellow alert for expected fatalities and damage. "Some casualties and damage are possible and the impact should be relatively localised," it said.
In the coastal town of Sigli people panicked and fled their houses to seek shelter away from the sea, despite no tsunami alert being issued. "We are now evacuating to Tijue because we are afraid of a tsunami," said Nilawati, one of those heading inland.
Indonesia experiences frequent seismic and volcanic activity due to its position on the Pacific "Ring of Fire", where tectonic plates collide. Aceh lies on the northern tip of Sumatra island, which is particularly prone to quakes. The last one struck in July.
Selina Sumbung, chairperson of a local partner of Save the Children, said it was still too early to know exactly how severe the humanitarian impact will be. She said roads and ports had been damaged "which may result in further challenges in delivering aid".
"We're particularly concerned about the impact on children. Earthquakes can be extremely frightening, and children's psychosocial wellbeing will be an important part of the recovery process," Sumbung said.
[Associated Press and Agence France-Presse contributed to this report.]