Although the oil-producing South American nation frequently suffers seismic shudders because of its position on the Pacific rim's Ring of Fire, the quake -- though it lasted just one minute -- was the worst in nearly 40 years in Ecuador.

The quake wrecked buildings, toppled power lines and sent terrified residents running from their homes when it struck a coastal zone popular with tourists.

Some 100 inmates in a prison in the western town of Portoviejo escaped when the quake shook their facility, Justice Minister Ledy Zuniga tweeted.

About 30 of them had been recaptured, some had returned voluntarily and police were hunting for the others.

Elsewhere in hard-hit Portoviejo, the odor of decaying bodies started to fill the tropical air as rescuers raced to find survivors.

 "We have already recovered three dead and we believe there are 10 to 11 people still trapped," said one worker digging through the debris of what used to be a six-story hotel called El Gato.

Officials have declared a state of emergency in the worst-hit provinces, and a national state of "exception," both of which suspend certain civil rights and liberties to allow security forces and officials to react faster.

'Lots of dead bodies'  

Among the worst-hit towns was Pedernales, where Mayor Gabriel Alcivar estimated there were up to 400 more dead yet to be confirmed, many under the rubble of hotels that collapsed.

"Pedernales is devastated. Buildings have fallen down, especially hotels where there are lots of tourists staying. There are lots of dead bodies," he told local media.

Soldiers patrolled the beach town, and the Red Cross and the army had set up a center to treat the injured and receive bodies.

Two Canadians were among those killed by the quake, their country's government told AFP.

Ecuador's Geophysical Office reported "considerable" structural damage as far away as Guayaquil, Ecuador's biggest city with more than two million people, which is 350 kilometers (220 miles) away.

In the town of Abdon Calderon, near Portoviejo, 73-year-old resident Nelly, who would not give her last name, told AFP in tears that she rushed into the street after the quake and saw that the covered market had collapsed.

"There was a person trapped who screamed for help, but then the screaming stopped. Oh, it was terrible," she said.

Neighboring Colombia -- which also felt the quake but emerged unscathed -- has dispatched aid and emergency workers to help in the rescue effort, as have Mexico and El Salvador.

Some 200 aftershocks of lesser intensity have followed the quake.

'Oil facilities undamaged'

The epicenter of the quake was 170 kilometers (106 miles) northwest of the capital Quito, which suffered relatively little damage beyond cracks in walls and a power outage.

Officials said the oil infrastructure of Ecuador, an OPEC member, seemed intact.

Ecuador has been rocked by seven earthquakes of magnitude 7.0 or higher in the region of Saturday's quake since 1900, the US Geological Survey said. One in March 1987 killed about 1,000 people.

David Rothery, a professor of geosciences at Britain's Open University, said the 7.8 magnitude meant that "the total energy involved was probably about 20 times greater" than the magnitude 7.0 earthquake that killed at least 41 people in southern Japan on Saturday.

He said there was no causal link between the two quakes. (AFP)