UPDATE: At least 77 people were killed when a powerful 7.8-magnitude earthquake struck Ecuador, destroying buildings and sending terrified residents dashing from their homes, authorities said late Saturday.
Vice-President Jorge Glas said the death toll will likely rise further in what he called the "worst seismic movement we have faced in decades."
EARLIER REPORT: Powerful 7.8 quake rocks Ecuador; Tsunami warning
At least 28 people were killed by a strong 7.8-magnitude earthquake that struck northwestern Ecuador on Saturday, the country's Vice President Jorge Glas said.
"We have 16 people dead in the city of Portoviejo, 10 in Manta and two in the province of Guayas," he told a news conference. He added that a state of emergency had been declared nationwide.
A powerful 7.8-magnitude earthquake rocked Ecuador Saturday, sending high-rises swaying in the country's biggest city of Guayaquil and knocking out power in much of the capital Quito, authorities said.
A tsunami warning was issued for local coasts but there were no immediate reports of casualties.
"There is considerable (structural) damage in the area near the epicenter as well as points as far away as Guayaquil," the Geophysical Office (IG) said.
President Rafael Correa, on a visit to the Vatican, sent a message of support on Twitter.
"Authorities are already out evaluating damage and taking action" as needed," he said.
Vice President Jorge Glas also said on Twitter that a national emergency committee had been activated.
"I am on the way to the national emergency center to coordinate operations nationwide. We will keep you informed," he said.
With a depth of 10 kilometers (six miles), the quake struck at 2358 GMT about 173 km west-northwest of Quito and just 28 kilometers south-southeast of Muisne, the US Geological Survey said.
A tsunami warning was issued for local coasts.
"Based on the preliminary earthquake parameters, hazardous tsunami waves are possible for coasts located within 300 kilometers of the earthquake epicenter," the Pacific Tsunami Warning Center said.
Buildings swayed in Quito but authorities did not immediately report injuries or damage.
The strong movement was felt in northern and southern parts of the metro Quito area, knocking out electricity in many areas.
Cristina Duran, 45, grabbed her three pets and stood under a large doorway to avoid shards of glass falling from shattered windows.
"I was frightened. And I just kept asking for it to be over," she told AFP.
Panic on the streets
Aftershocks kept rattling the country, as structural damage was reported in the coastal provinces of Manabi and Guayas.
At the airport in the port city of Guayaquil passengers awaiting flights dashed out of terminals when they felt the shaking.
"Lights fell down from the ceiling. People were running around in shock," said Luis Quimis, 30, who was waiting to catch a flight to Quito.
In northern Quito, people ran out of their homes frightened, as power lines swayed back and forth and cables danced.
"Oh, my God, it was the biggest and strongest earthquake I have felt in my whole life. It lasted a long time, and I was feeling dizzy. I couldn't walk. ... I wanted to run out into the street, but I couldn't," said Maria Torres, 60.
In fact, two earthquakes jolted the same area just 11 minutes apart, the USGS said. The first had a magnitude of 4.8 and the second of 7.8.
The quake also rattled northern Peru, according to authorities there.
The major jolt came as rescuers in Japan were racing against the weather and the threat of more landslides to reach people still trapped by two big earthquakes that hit that country's south.
At last 41 people are known to have died in the double disaster, with at least six still missing -- feared buried in shattered houses or under torrents of mud.