"Jamil hospital collapsed and thousands of people are trapped in the rubble of buildings," Pakaya said.
The magnitude 7.6 quake was centred 32 miles north-west of the city in western Sumatra, said the US geological survey.
An earlier quake prompted a tsunami that struck the Pacific islands of Samoa and American Samoa, killing more than 100 people.
Local reports said the Indonesian quake brought down buildings and bridges, damaged houses and started fires. There were no immediate reports of fatalities but several people were reported injured.
"A number of hotels in Padang have been destroyed," Rahmat Triyono, of the Indonesian geophysics and meteorology agency was quoted as saying by the Jakarta Post. "Up to now we haven't been able to reach Padang. Communications have been cut."
The Pacific Tsunami Warning Centre issued an alert but later cancelled it. Tremors from the quake were said to have been felt in Malaysia and Singapore.
A 6.2-magnitude aftershock followed the initial quake about 22 minutes later, the meteorological agency said.
The earthquake came hours after another quake triggered a tsunami that left at least 100 people dead on the Pacific islands of Samoa and American Samoa.
A resident described the scene to Indonesia's Metro Television. "For now I can't see dead bodies, just collapsed houses. Some half-destroyed, others completely. People are standing around too scared to go back inside. They fear a tsunami.
"No help has arrived yet. I can see small children standing around carrying blankets. Some people are looking for relatives but all the lights have gone out completely."
Other eyewitness accounts said people fled on to the streets as buildings collapsed.
"Hundreds of houses have been damaged along the road," Reuters quoted a witness as saying. "There are some fires, bridges are cut and there is extreme panic here because water pipes are broken and there is flooding in the streets."
Padang, a city of 900,000 people, sits on one of the world's most active faultlines along the "ring of fire", where the Indo-Australia plate and the Eurasia tectonic plate grind together to cause frequent tremors and, occasionally, large earthquakes.
The same faultline caused the 2004 tsunami in which 232,000 people died in Indonesia, Thailand, Sri Lanka, India and other countries across the Indian Ocean.
"Padang sits right in front of the area with the greatest potential for an 8.9 magnitude earthquake," Danny Hilman Natawidjaja, a geologist at the Indonesian Science Institute, said earlier this year. "The entire city could drown in a tsunami triggered by such a quake,." he added.
