The death toll in the earthquake that struck off the coast of Ecuador as of Saturday had increased to 77, local media reported, citing Ecuadorian Vice President Jorge Glas.

The number of deaths would "unfortunately rise in the coming hours," Glas said in televised comments.

The government has declared a nationwide state of emergency and activated its Emergency Operations Committee, which is tasked with coordinating emergency services.

The strong quake occurred at 18:58 local time (2358 GMT) and was centered just off the country's northwest coast at a shallow depth of 19 km, according to the U.S. Geological Survey (USGS), which originally put the quake at a magnitude of 7.4 and then raised it to 7.8.

Ecuador's Institute of Geophysics put the quake's magnitude at 6.5 and the depth at 10 km.

In the capital city of Quito, the quake was felt for about 40 seconds and people fled to streets in panic. Quito is located about 170 km from the quake's epicenter. Some neighborhoods in the capital were out of power or telephone services.

In the biggest port city of Guayaquil, an overline bridge collapsed on top of a car and the roof of a supermarket buckled. In the coastal city of Manta, the airport was closed after the control tower suffered severe damages.

Several aftershocks, some as strong as 5.6 on the Richter scale, occurred in the hour after the first quake.

The Pacific Tsunami Warning Center said hazardous tsunami waves are possible for some coasts.

Ecuador is located in a region with frequent volcanic eruptions and earthquakes.