JAKARTA - A magnitude 7.7 earthquake shook Indonesia's northwest island of Sumatra early Wednesday, triggering a small tsunami, snapping power lines and sending panicked residents rushing for higher ground.

There were scattered reports of injuries, but only minor damage in most areas.

The quake struck at 5:15 a.m. (2215 GMT) and was centered undersea 125 miles (205 kilometers) northwest of the coastal town of Sibolga in Sumatra at a depth of 19 miles (31 kilometers), the US Geological Survey said. It had earlier said the quake measured 7.8.