The Antara news agency reports about 60 boats were swept onshore by the ocean surge, which also caused damage to an ice factory beyond anything inflicted by the quake.
The U.S. Geological Survey said the temblor struck near Sinabang, in Sumatra’s Simeulue district, at 5:15 a.m. local time.
The epicenter was located just offshore, prompting the area's tsunami-wise population to rush to higher ground. Three moderate aftershocks occurred following the initial jolt.
A reporter from the country’s Metro TV reported that he tumbled off his motorbike when the quake struck. He said the ground motion was so powerful that it left electricity poles swaying for minutes after the shaking stopped.
Disaster officials said widespread power failures were due to about 80 percent of the small electricity substations in North Sumatra province being damaged by the quake. The shaking downed utility poles, broke roof tiles and shattered glass windows, according to local authorities. Most of those injured were struck by falling objects or flying debris.
A 7.6 magnitude offshore quake last October killed more than 1,000 people in the nearby city of Padang. The devastating 2004 quake and Indian Ocean tsunami also originated near Wednesday morning’s epicenter.