People stay outside their houses after an earthquake in the city of Quito, capital of Ecuador, on April 16, 2016. Some 28 people have been killed in the 7.8-magnitude earthquake that struck Ecuador Saturday, Ecuadorian Vice President Jorge Glas said. (Xinhua/Santiago Armas)

At least 28 people were killed as a 7.8 magnitude earthquake struck off the coast of Ecuador Saturday, Ecuadorian media reported.

Vice President of Ecuador Jorge Glas announced shortly after the quake that at least 28 people have been killed so far: 16 people in the city of Portoviejo, 10 in the city of Manta and two in the Guayas province.

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 the streets in panic. Quito is located about 170 km from the quake's epicenter. Some neighborhoods in the capital were without power or telephone service.

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.