A disastrous relief spokesman said, at least 200 are dead and thousands are said to be buried under the rubble.
According to reports, the death toll is likely to rise because there are many people still trapped in buildings, shops and hotels.
Priyadi Kardono, a spokesman for the National Disaster Management Agency, said that about 500 buildings collapsed in Padang, a regional capital of 900,000 people.
During the quake, the shaking was so intense that people crouched or sat on the street to avoid falling. Thousands tried to flee the coast in cars and on motorbikes, Kardono said.
"This is a high-scale disaster, more powerful than the earthquake in Yogyakarta in 2006, when more than 3,000 people died," Health Minister Siti Fadilah Supari said.