Rescue workers and ordinary people are mounting an increasingly desperate search for survivors of two deadly earthquakes that cut a path of destruction through northern Venezuela.

As the death toll rose, and with a medical system hollowed out by a decade-long economic depression, people clawed through brick and concrete with their bare hands as the Venezuelan authorities and emergency teams from around the world struggled to contend with the scale of the disaster.

At least 920 people have been killed in the back-to-back earthquakes on Wednesday and more than 3,300 people injured, Jorge Rodríguez, the leader of the National Assembly, said on Friday. Those numbers are expected to rise further. Scores of people were still believed trapped in the rubble.

How big were the quakes?

Seismologists recorded the earthquakes’ epicenters in the Venezuelan state of Yaracuy, west of Caracas. Tremors were felt more than 100 miles away.

The initial one hit at 6:04 p.m. Eastern time on Wednesday with a magnitude of 7.2. The epicenter was near San Felipe, a city of about 220,000 people.

Around 39 seconds later, a second, stronger quake with a magnitude of 7.5 hit nearby. It was the most forceful earthquake to strike Venezuela since 1900.

Scientists pointed to two factors that made the quakes especially devastating.

They came in quick succession, a rare “doublet” as the Caribbean tectonic plate ground against the South American one. And they struck at a relatively shallow depth, according to the United States Geological Survey, making them particularly dangerous.

Two smaller follow-up earthquakes were recorded near Caracas, and seismologists assessed that at least one aftershock at a magnitude of 5.0 or greater over the next week is likely.

How many people have died?

Mr. Rodríguez, the National Assembly leader, said on Friday afternoon that the death toll had risen to at least 920 people, with 3,360 injured.

The strongest tremors struck the northern states of Yaracuy, Carabobo, Aragua and La Guaira, which include some of Venezuela’s most populous areas.

According to the U.S. Geological Survey, many houses in those areas are made of unreinforced brick masonry and adobe blocks, which are particularly vulnerable to earthquakes.

In some neighborhoods of Caracas, buildings collapsed and the power went out. Witnesses described buildings shaking violently, windows rattling and water pipes bursting.

Photos and videos verified by The New York Times show concrete buildings reduced to rubble and others severely damaged. In the port city of La Guaira, buildings as tall as 10 stories high collapsed, and high-rise tower blocks were seen tilting.

How are emergency crews responding?

Venezuelan authorities have mobilized hundreds of emergency responders to look for survivors. President Delcy Rodríguez declared a state of emergency, called on doctors and nurses to report to work to care for the injured and said that hotels and shelters would be opened for those left without homes.

At the site of one collapsed building in El Paraíso, a neighborhood of Caracas, rescuers pulled a young girl and a dog from the rubble. In the capital’s Chacao municipality, the mayor said that at least 22 people had been rescued.

Rescue teams from around the world were arriving in the country on Friday to join the effort to retrieve survivors and bodies from the rubble. The United States and several Latin American countries said they would send humanitarian aid and rescue personnel. Late Thursday, a Marine Corps major general landed in Caracas to direct the U.S. military’s relief efforts, according to United States Southern Command.

Venezuela’s fragile infrastructure — including rail, electricity and health care systems that have suffered from years of corruption and mismanagement — were also hammered by the quakes, further hampering response efforts.

The earthquakes caused over 100 buildings to collapse in the city of La Guaira, the U.N.’s main humanitarian agency said, overwhelming local authorities.

What is the political situation in Venezuela?

Venezuela is reeling from years of economic turmoil and crippling U.S. sanctions, and the earthquakes pose an immediate challenge for the president, Ms. Rodríguez.

In an audacious raid in January, U.S. forces captured and deposed the autocratic president, Nicolás Maduro, transporting him to the United States to face federal drug charges. President Trump handpicked Ms. Rodríguez as his successor and promised that the change would “unleash prosperity” by reviving Venezuela’s oil industry.

Six months on, there has been little sign of dramatic economic turnaround under Ms. Rodríguez, whose approval rating fell to 25 percent in May. Public coffers remain largely empty, leaving the government ill equipped to fund basic services.

Although the Trump administration has issued special exemptions from sanctions for companies interested in doing business in Venezuela, none has publicly committed to bringing significant capital into the country. Annual inflation is falling but remains the world’s highest, the currency has continued to decline in value, and though wages have increased, they are still too low to to lift many out of destitution.