Debris of a house remain in the floor after an earthquake in Quito, Ecuador, on April 16, 2016.[Photo/Xinhua]

GUAYAQUIL, Ecuador - Ecuador launched rescue operations on Sunday after its biggest earthquake in decades killed at least 77 people, caused devastation in coastal populations, and left an unknown number trapped in ruins.

The 7.8 magnitude quake struck off Ecuador's Pacific coast on Saturday night and was felt around the Andean nation of 16 million people, causing panic in the capital Quito and collapsing buildings in the large commercial city of Guayaquil.

Nearly 600 people were injured.

Northwestern coastal areas nearest the quake were worst affected, including Pedernales, a tourist spot with beaches and palm trees, and nearby Cojimies. But information was scant from there due to poor communications and transport chaos.

"There are people trapped in various places and we are starting rescue operations," Vice President Jorge Glas said on Sunday morning before boarding a plane to the area.

The toll of 77 dead and 588 injured was bound to rise, he said. A state of emergency was declared in six provinces.

"There are villages that are totally devastated," Pedernales' major Gabriel Alcivar, said in a radio interview, adding that "dozens and dozens" had died in the rustic zone.

"What happened here in Pedernales is catastrophic."

In Guayaquil, Ecuador's largest city, rubble lay in the streets and a bridge fell on top of a car.

"It was terrifying, we were all scared and we're still out in the streets because we're worried about aftershocks," said Guayaquil security guard Fernando Garcia.

About 13,5000 security force personnel were mobilized to keep order around Ecuador, and $600 million in credit from multilateral lenders was immediately activated for the emergency, the government said.