President Michelle Bachelet said there were 78 confirmed deaths and that more were possible. Telephone and power lines were down, making it difficult to make an early assessment of the damage, but serious damage was reported in two southern cities.
"Never in my life have I experienced a quake like this, it's like the end of the world," one man told local television from the city of Temuco, where the quake damaged buildings and forced staff to evacuate the regional hospital.
Chilean television and radio stations said several buildings collapsed in the city of Curico and that there was damage to buildings in the historic center of the capital Santiago, about 200 miles north of the epicenter.
The capital's international airport was forced to close, a highway bridge collapsed and chunks of buildings fell into the street. Television pictures showed cars crushed when part of a multi-storey parking garage collapsed.
Broken glass and masonry were strewn across roads in Santiago and several strong aftershocks rattled jittery residents in the hours after the initial quake.
In the moments after the quake, people streamed onto the streets of the capital, hugging each other and crying.
There were blackouts in parts of Santiago and communications were still down in the area closest to the epicenter. Emergency officials said buildings in the historic quarters of two southern cities had been badly damaged.
Bachelet urged people to stay calm and to remain at home to avoid road accidents. "With a quake of this size we undoubtedly can't rule out more deaths and probably injuries," she said.
Bachelet said a huge wave swept into the southern island of Juan Fernandez, and radio stations said it caused serious damage.
The Pacific Tsunami Warning Center said the tsunami may have been destructive along the coast near the epicenter "and could also be a threat to more distant coasts.
According to a 2002 census, Concepcion is one of the largest cities in Chile with a population of around 670,000.
Chile's main copper producing region and some of the world's largest copper mines are in the far north of the country near its border with Peru, but there are also major copper deposits near Santiago. Officials said roads to the important Los Bronces mine, owned by Anglo American Plc, near the capital were blocked.
Chile produces about 34 percent of world supply of copper, which is used in electronics, cars and refrigerators.
In 1960, Chile was hit by the world's biggest earthquake since records dating back to 1900.
The 9.5 magnitude quake devastated the south-central city of Valdivia, killing 1,655 people and sending a tsunami which battered Easter Island 2,300 miles off Chile's Pacific seaboard and continued as far as Hawaii, Japan and the Philippines.
Saturday's quake shook buildings as far away as Argentina's Andean provinces of Mendoza and San Juan. A series of strong aftershocks rocked Chile's coastal region from Valdivia in southern to Valparaiso, about 500 miles to the north.
The tsunami warning center said there was a possibility the U.S. state of Hawaii could be elevated to watch or warning status.