A powerful 6.7-magnitude earthquake jolted Chile's northern coast Sunday, US geologists said, generating a small tsunami and prompting authorities to evacuate three cities. The quake struck at 6:16 pm (2116 GMT), according to the US Geological Survey, which had originally put the magnitude at 7.0. Located 60 kilometers (38 miles) west-northwest of the port city of Iquique, the quake was 20 kilometers deep, the USGS said in an update. It was followed by a series of aftershocks. The Pacific Tsunami Warning Center said in a bulletin that "sea level readings indicated a tsunami was generated." Tsunami wave activity was measured at 28 centimeters (one foot). "It may have been destructive along coasts within 200 km of the earthquake epicenter," the center added. "Danger to boats and coastal structures can continue for several hours due to the rapid currents." Chilean authorities ordered precautionary evacuations of 100,000 people in the northern coastal cities of Arica, Iquique and Antofagasta due to fears of a "minor" tsunami. The evacuation alert lasted about three hours. "Everything worked flawlessly. Chile is a seismic country and people reacted appropriately," Undersecretary of the Interior Mahmud Aleuy told reporters. In February 2010, central and southern Chile were hit by a powerful earthquake of 8.8-magnitude followed by a tsunami that devastated dozens of towns. The quake left more than 500 dead and $30 billion in damage to infrastructure. Chile is one of the most seismically active countries in the world, and a large earthquake had long been expected in the north of the country.