A TV grab shows a crushed car in a parking garage in Concepcion Chile following the earthquake early Saturday morning. (AP Photo)
One of the largest earthquakes on record killed at least 300 people in Chile and sent giant waves roaring across the Pacific Ocean that forced Japan to issue a major tsunami alert almost a day later.
In an address to the nation, President Michelle Bachelet said two million Chileans had been affected but, after touring the worst-hit areas by plane, she found it hard to spell out the magnitude of the disaster that struck on Saturday.
"The power of nature has again struck our country," Bachelet said, declaring six of Chile's 15 regions "catastrophe zones" in the aftermath of the 8.8-magnitude quake.
Highways in the South American nation of 16 million were sliced to pieces, bridges imploded and buildings collapsed as the 8.8-magnitude earthquake struck overnight some 325 kilometres southwest of the capital Santiago.
"This is a catastrophe of immense proportions, so it will be very difficult to give precise figures," Interior Minister Edmundo Perez Yoma said. Officials later said at least 300 people had been killed.
Waves well over two metres high crashed into the Chilean coast after the quake struck at 3:34 am (1204 IST) and tore out into the Pacific, killing at least five people in the remote Robinson Crusoe islands.
In the Chilean port of Talcahuano, trawlers were sent shooting inland to the town square where they lay oddly marooned next to abandoned cars.
About 50 countries and territories along an arc stretching from New Zealand to Japan braced for giant waves, five years after the Indian Ocean tsunami disaster that killed more than 220,000 people.
The ominous sound of evacuation sirens blared in Hawaii, French Polynesia and the South Pacific as a tsunami raced around the "Ring of Fire", but warnings were later cancelled everywhere apart from Japan and far-east Russia.
The Japan Meteorological Agency warned that waves of up to three metres could hit the northern coastal areas and issued tsunami warnings for up to two meters along the entire Pacific coastline of the Japanese archipelago.
The massive quake plunged much of the Chilean capital Santiago into darkness, snapping power lines, severing communications. The international airport was closed after sustaining significant damage to the terminal.
Many Chileans were still in nightclubs partying at the start of the weekend when the quake struck before dawn, ripping up roads, bringing roofs crashing down and toppling power lines.
"It was the worst experience of my life," said 22-year-old Sebastian, standing outside his house in eastern Santiago.
"Friends who were at clubs said it was pandemonium," said Santiago resident Maren Andrea Jimenez, an American expert working for the United Nations. "It was scary! Plaster began falling from the ceiling. My dogs freaked out."
President Barack Obama said the United States "stands ready to assist in the rescue and recovery efforts, and we have resources that are positioned to deploy should the Chilean government ask for our help."
"Early indications are that hundreds of lives have been lost in Chile and damage is severe. On behalf of the American people, Michelle and I send our deepest condolences to the Chilean people," he said at the White House.
Despite officials saying up to 1.5 million homes could be affected, Chile's Foreign Minister Mariano Fernandez asked countries that had offered aid to hold off until local authorities could assess the emergency needs.
Chile does not want "aid from anywhere to be a distraction" from disaster relief, Fernandez said, adding: "Any aid that arrives without having been determined to be needed really helps very little."
US Secretary of State Hillary Clinton, due to leave shortly on a Latin American tour that includes Chile, said she was in close contact with Bachelet and that "our thoughts and prayers" went out to the victims.
The European Union said it would provide three million euros (four million dollars) in immediate assistance. Unlike Haiti, struck by a devastating earthquake last month, Chile is one of Latin America's wealthiest countries.
The US Geological Survey said it had recorded more than 51 aftershocks ranging from 4.9 to 6.9 since the quake.
A second 6.1-magnitude quake, said to be an entirely separate event killed two people in neighbouring Argentina.