At least 77 people have died and more than 570 are injured in the magnitude-7.8 quake, which was centred on Ecuador's sparsely populated fishing ports and tourist beaches, 170 kilometres (105 miles) north west of Quito.
Vice president Jorge Glas gave the updated death toll early on Sunday at a press conference. Late on Saturday, he said there were reports of deaths in the cities of Manta, Portoviejo and Guayaquil - all several hundred kilometres from where the quake struck shortly after nightfall.
"We're trying to do the most we can but there's almost nothing we can do," said Gabriel Alcivar, mayor of Pedernales, a town of 40,000 near the quake's epicentre.
The Salvation Army said it was distributing food and water to people affected by the quake.
#Ecuador: The Salvation Army is helping people evacuated from homes damaged in the 7.8-magnitude #earthquake. Food/water being distributed.
— Salvation Army IHQ (@SalvArmyIHQ) April 17, 2016
President Rafael Correa signed a decree declaring a national emergency and rushed home from a visit to Rome. He urged Ecuadorians to stay strong while authorities handle the disaster and hoped to be back in the country by Sunday afternoon.
The quake was the strongest to hit Ecuador since 1979, Mr Glas said.
An emergency situation was declared in six of Ecuador's 24 provinces, while sports events and concerts were cancelled until further notice nationwide.
"It's very important that Ecuadorians remain calm during this emergency," Mr Glas said from Ecuador's national crisis room.
The United States Geological Survey originally put the quake at a magnitude of 7.4 but then raised it to 7.8. It had a depth of 19 kilometres (12 miles). At least 36 aftershocks followed, one as strong as 6 on the Richter scale, and authorities urged residents to brace for even stronger ones in the coming hours and days.
The quake comes on the heels of two deadly earthquakes across the Pacific, in the southernmost of Japan's four main islands. A magnitude-6.5 earthquake struck on Thursday near Kumamoto, followed by a magnitude-7.3 earthquake just 28 hours later. The quakes have killed 41 people and injured about 1,500, flattened houses and triggered major landslides.