“High casualties” are feared after back-to-back powerful earthquakes struck Venezuela, bringing down buildings in the capital of Caracas.

Witnesses ‌reported ⁠tremors late on Wednesday (local time) when a 7.1-magnitude quake hit, followed just 40 seconds later by a second with a magnitude of 7.5.

“Several walls in my building ​broke ​open or cracks formed,” one ​witness in Valencia, west of ‌Caracas, told Reuters.

“As soon as it stopped [shaking], my husband and I evacuated.”

The first tremor struck the area of Montalbán at a depth of 13.2 kilometres at 6.04pm local time, according to the US Geological Survey. The second was 10-kilometres deep, with its epicentre 16 kilometres south-west of the city of Morón.

“High casualties and extensive damage are ‌probable and the disaster is likely widespread,” the USGS said, initially estimating a death toll as high as 100,000.

Authorities did not immediately provide official estimates for deaths or injuries.

“We have buildings, homes and houses which have collapsed and we are taking care of things with everything we have available in terms of security, civil assistance,” Interior Minister Diosdado Cabello said on state television.

“The fire department, police all have been activated.”

Video footage showed emergency workers climbing through the ruins of a collapsed building in the capital as night fell ‌and distraught relatives seeking help ‌for loved ones.

The US Tsunami Warning System initially issued an alert for Venezuela, the US Virgin Islands and the British Virgin Islands. It also said islands off the coast of Venezuela – Aruba, Curacao and Bonaire – were at risk.

The warning was later cancelled.

Cabello said the initial quake could be felt in several states, adding the Altamira neighbourhood in Caracas had “alarming situations” with collapsed homes and buildings.

He urged people to remain outside as aftershocks could further damage some structures.

The first tremor hit at what would normally have been peak hour. But many Venezuelans were at home, celebrating a public holiday commemorating an 1821 military victory that secured Venezuela’s independence from Spain.

“As soon as it started, we began hearing people screaming,” said Astrid Ramirez, a 41-year-old publicist in western Caracas. “Everyone was running down the stairs.”

Damage is believed to be widespread after the twin earthquakes. Photos: X

Maria Romero, an 80-year-old pensioner in Caracas’ south, said police helped her evacuate her building.

“This earthquake was horrible, even worse than the one in 1967,” she said.

A 6.6-magnitude quake struck Caracas in 1967, killing more than 200 people and destroying buildings in the middle-class neighbourhood of Palos Grandes and the upper-class area of Altamira. Both neighbourhoods were again affected by Wednesday’s twin tremors.

According to videos from Reuters witnesses, there were fire trucks on the streets in ⁠Caracas, and the facades of some ‌buildings ​had suffered significant damage.

Many residents in Caracas lost power or internet service in the immediate aftermath.

One witness said that cracks had formed up the side of ​their apartment and glass in the entry had shattered. Power went down shortly after, they said.

Another witness, Coro Martinez, who lives in eastern Caracas told Reuters of a “very loud crash”.

“Things fell in the house, jugs inside the refrigerator. I’ve never experienced anything like it,” the 56-year-old said.

Another resident, a ​41-year-old office worker who declined to be named, said she received an earthquake alert on her phone just before the shaking intensified.

“It was a normal afternoon, and suddenly ​my phone sounded ‌an earthquake alert,” she said.

“As I picked it up and started listening to what it was saying, I first felt light shaking. Then, in less than two seconds, everything ​started moving.”

Video filmed at the Hospital de Clinicas Caracas showed a darkened hallway with ceiling panels hanging by cables and pieces of plaster scattered across the floor.

Other videos on social media appeared to ​show ​significant damage at Venezuela’s main airport, while residents reported collapsed buildings in La ​Guaira, a coastal city near Caracas. Reuters could not immediately verify the footage from ‌the airport and La Guaira.

Venezuela is in a seismically ​active zone where the Caribbean Plate meets the South American Plate.

-with AAP