JAKARTA (BNO NEWS) — A powerful earthquake struck off the coast of Indonesia’s northern Sumatra on early Wednesday, seismologists said, creating a tsunami that may have affected local coastlines.

The 7.7-magnitude earthquake at 5.15 a.m. local time was centered about 200 kilometers (125 miles) west-northwest of Sibolga on Sumatra. It struck about 31 kilometers (19.3 miles) deep, making it a shallow earthquake.

The Badan Meteorologi Klimatologi dan Geofisika (BMKG), Indonesia’s seismological agency, said the earthquake had tsunami potential and immediately issued a tsunami warning.

The Pacific Tsunami Warning Center did not issue a warning, but instead issued a – less severe – tsunami watch. “A destructive widespread tsunami threat does not exist based on historical and tsunami data,” a bulletin from the agency read, indicating other countries are not at risk. “However, there is the possibility of a local tsunami that could affect coasts located usually no more than a hundred kilometers from the earthquake epicenter.”

The agency later confirmed a tsunami was in fact generated. “Sea level readings indicate a tsunami was generated,” a bulletin read. “It may have been destructive along coasts near the epicenter.” Tsunami wave activity of 14 cm (0.5 ft) was recorded off Teluk Dalam, a sub-district in North Sumatra. Fourteen centimeters does not indicate the height of the actual tsunami, as that was recorded off the coast and tsunamis are known to grow as it approaches the coastline.

At least four moderate aftershocks shook the region after the first earthquake, BMKG reported. Those had magnitudes of 5.0, 4.9, 5.1 and 5.0.

The Kompas newspaper reported there were power outages in the area after the quake, but there was no immediate word on possible casualties.

According to a U.S. Geological Survey chart, about 33,000 people may have been exposed to ‘severe’ shaking which could result in ‘heavy’ damage to vulnerable structures. Some 457,000 others may have received ‘very strong’ shaking while nearly 1.5 million people may have experienced strong shaking.

A 9.0-magnitude earthquake on December 26, 2004 struck about 167 kilometers northwest of Wednesday’s earthquake. That earthquake and a resulting tsunami killed nearly 230,000 people.

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