The U.S. Geological Survey said the quake was very shallow, only 6.2 miles (10 km) below the seabed, and struck at 6:46 p.m. local time (2346 GMT) 62 miles (99 km) northwest of the mining port of Iquique, near the Peruvian border.
The Chilean navy said the first tsunami wave had hit the coast within 45 minutes of the quake.
"An earthquake of this size has the potential to generate a destructive tsunami that can strike coastlines near the epicenter within minutes and more distant coastlines within hours," the Pacific Tsunami Warning Center said.