Rescue workers and desperate residents dug for survivors in the rubble of large apartment buildings and flattened homes on Thursday after back-to-back major earthquakes struck Venezuela, a country already reeling from decades of economic and political upheaval.

The Venezuelan government said that at least 188 people had been killed and more than 1,500 injured in the two quakes. The first, with a magnitude of 7.2, struck west of the capital, Caracas, on Wednesday just after 6 p.m. local time. It was followed by another, much stronger one measuring 7.5 just 39 seconds later.

The rare one-two punch, known as a doublet, was one of the most powerful tectonic events to strike Venezuela in the past century, and the death toll was virtually certain to rise as rescuers began to reach hard-hit areas and remote hillside towns.

La Guaira, a port city north of Caracas, appeared to have taken one of the heaviest blows. Entire buildings there had crumbled to the ground. Some apartments had only walls remaining, making them look skeletal.

When Yorliana Colmenares stood near one building that had been reduced to rubble, she heard tapping noises on Thursday morning.

Her boyfriend was trapped inside, she believed. But no rescue workers, firefighters or medical workers had arrived, so residents were digging by themselves though crushed walls and knotted wire and dust.