The biggest earthquake in Ecuador in decades has killed 272 people -- but that toll will 'certainly' rise even further, the president said on Sunday as overwhelmed rescuers struggled to pull survivors out of the destruction.

The 7.8-magnitude quake struck the small, oil-producing South American nation late Saturday, shattering hotels and homes along its Pacific coast popular with tourists and reducing several towns to rubble.

More than 2,000 people were injured as structures tumbled during the quake or its dozens of aftershocks.

The capital Quito, farther inland, escaped with cracked walls and power outages, and the country's strategic oil facilities appeared unscathed, officials said.

But along the coast, the devastation prompted neighboring Colombia, as well as quake-experienced Mexico and El Salvador, to rush in rescue personnel to help out.

In Portoviejo, a city 15 kilometers (10 miles) from the coast, the temblor knocked down walls in a prison, allowing 100 inmates to escape.

Some were recaptured or returned later, but police were hunting the others, Justice Minister Ledy Zuniga tweeted.

Elsewhere in hard-hit Portoviejo, the stench of decaying bodies began 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.

- State of emergency -

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.

President Rafael Correa visited the disaster zone last Sunday, after cutting short an official trip to the Vatican and flying home.

He said the latest toll of 272 dead "will certainly rise and probably in a considerable way" in the hours ahead.

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.

Colombia's foreign ministry said five Colombians had also died.

In 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.

- Ring of Fire -

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.

Although Ecuador frequently suffers seismic shudders because of its position on the Pacific rim's Ring of Fire, the weekend's quake -- which lasted a full minute -- was the worst to hit it in nearly 40 years.

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.

International concern and sympathy -- and offers to assist -- have flowed in.

Pope Francis urged prayers for the victims.

US Secretary of State John Kerry and European Union chief diplomat Federica Mogherini expressed condolences and said they were ready to help.