The Indonesian island of Sumatra has been hit by a powerful earthquake, which has left dozens dead and many injured.
The quake struck late in the morning, at 1049 local time (0349 GMT), while many people were at work or school.
People inside buildings rushed outside, fearing the structures would collapse.
Hospitals have been overwhelmed by the numbers of injured
In coastal Padang, capital of West Sumatra province, many people fled to higher ground, with memories of 2004's deadly earthquake-triggered tsunami still fresh in their minds.
A female office worker in Padang, who was working on the second floor of her building when the initial tremor struck, told the BBC's Indonesian service that everyone in her building ran outside as soon as they could.
"Our floor was actually swaying away for about five minutes," she said.
"People were panicky with the thought [that a] tsunami might follow suit, although they have been informed through continuous broadcast along the streets of Padang to [tell] people that there won't be any tsunami as the quakes were originated from the land and not from the sea, but the people of Padang were still unconvinced."
Another Padang resident, Asmiarti, told Reuters news agency of the fear she felt as the earthquake struck.
"It was really strong. I panicked, I ran out of the house just like the other neighbours," she said.
"When we got out, our bodies were still shaking and the trees were also shaking. We fear there would be a tsunami but there has been no announcement so far".
Officials have confirmed that hundreds of buildings have collapsed in Padang and several other towns, trapping an unknown number of people inside.
Elvin, also in Padang, described to the BBC the damage he saw immediately after the earthquake.
"I start to see houses, shops getting crushed, they were flattened to the ground and there were many people outside their houses, they were screaming, they were making groups in the street".
Emergency teams have attempted to fan out across the affected region to assess the damage.
But their efforts have been hampered by damaged roads and traffic jams from people fleeing the towns.
In Indonesia's capital, Jakarta, Vice-President Yusuf Kalla said he was pushing the rescue effort forward.
"The National Agency for Disaster Coordination will help the best they can if there's anything needed from Jakarta," he said.
"I trust the people and the government will be able to overcome the difficulties they're currently facing. The emergency response will soon be implemented and we should be able to see more clearly afterwards what has happened.
Solok, a rice-farming town south-east of Padang, was closer to the epicentre than Padang.
The town's mayor, Samsurahim, said hospitals were overwhelmed with wounded.
"Our priority is to handle the injured ones, including their families," he told Reuters. "We have set up six tents at a soccer field as emergency posts".
People are staying outside fearing more buildings may collapse
He said many people may still be trapped under rubble.
"The [rescue] process is going on... I cannot predict how many people are still trapped because the process is still on. However, there are many houses collapsed, and I believe that the inhabitants are in them."
A man in Solok described the panic and said the earthquake was like being in a storm-tossed ship.
"At that time everybody was rushing out of their houses trying to save themselves," he told the BBC.
"It was like the being in a ship where you were swayed around when there were big waves. The houses were all swaying away, so were the things inside and lots of the houses collapsed.
"I have witnessed the destruction of many people's houses as well as public social facilities like schools and mosques," he said.