The quake damaged houses and bridges, and caused fires in the city of Padang in Sumatra, a Reuters witness said on Wednesday.
"Hundreds of houses have been damaged along the road. There are some fires, bridges are cut and there is extreme panic here maybe because water pipes are broken and there is flooding in the streets," the witness said.
A witness also told local television that buildings collapsed.
The Pacific Tsunami Warning Center issued a tsunami alert for Indonesia, Malaysia, India and Thailand.
Shaking could be felt in high buildings in the capital, Jakarta, several hundred miles away and in neighboring Singapore and Malaysia.
The new quake comes on the heels of a magnitude 8 tembler that struck yesterday in the south Pacific Ocean, generating a tsunami that killed at least 99 people in the Samoa
Click for more on this earthquake from the USGS
The Associated Press contributed to this report.