The death toll from twin earthquakes rose Friday to 920 in Venezuela, where tens of thousands were reported missing as a desperate and slow-moving search for survivors was boosted by international rescue teams.

United Nations aid chief Tom Fletcher told AFP that more than 50,000 people were missing after two powerful earthquakes struck within a minute of each other on Wednesday night, flattening buildings in the north of the country.

The coastal area of La Guaira, near the capital Caracas, is the hardest hit, with one building after another crumpled by the magnitude 7.2 and 7.5 quakes.

A rescue team from Chile arrived at one residential complex in La Guaira, made up of four tall buildings housing hundreds of apartments that had largely been reduced to rubble. 

"Unfortunately, the collapse is total, and there is little chance of finding survivors. Efforts are now focused on recovering the bodies of the deceased," rescue team leader Nadiomar Polanco said at the site, which resembles many others in the city.

Elsewhere, family members, neighbors and volunteers resorted to using their bare hands to try to dig out survivors, bemoaning the lack of heavy machinery or official help to save those trapped alive.

"I am looking for my little Gael ... he was only five months old," said an anguished Marjosly Salazar, 40, whose 16-year-old daughter died in the quake. The baby and Salazar's cousin are both missing.

"Please, we need support here. We need machinery to start lifting the columns. We haven't seen any government officials here, none at all."

'Very complex'

AFP saw workers using sledgehammers to break through debris and calling for "absolute silence" to detect cries from survivors.

"It's a very, very complex emergency response," Fletcher told AFP, warning the death toll could rise significantly.

Aftershocks and destroyed buildings still posed significant dangers.

At one building in La Guaira, a rescue worker in a helmet implored people to get out of the way, warning of potential collapse.

"That building has already shifted 40 centimeters. If that building collapses, those of us here won't have a chance to get out of the way," he said. 

Oil-rich Venezuela is facing its worst earthquake in more than a century after more than a decade of economic collapse hollowed out hospitals and public services, driving millions to leave the country.

The country is still in a fragile transition six months after the United States ousted leader Nicolas Maduro.

Help arrives

Many families stood by helpless to pull out loved ones they could hear alive in the rubble.

"The authorities are useless; useless because the military should be here with all the heavy machinery they have," said La Guaira resident Argenis Mendez.

The UN humanitarian agency OCHA said search and rescue teams from at least 17 countries were being mobilized to help find survivors.

Spanish, Salvadoran, Swiss, Colombian, and Mexican rescue teams were already on the ground.

A senior US military official landed in Caracas to oversee Washington's relief efforts.

The United States said it was deploying two warships, transport planes and helicopters and mobilizing $150 million in aid. Washington has also suspended economic sanctions on Venezuela that could have hindered rescue operations, for a period of four months.

"Even before the earthquakes, millions of people across Venezuela were facing food insecurity, collapsing health services, protection risks, and limited access to basic services," the UN and other aid agencies said in a statement Friday.

"The international community must not allow this emergency to deepen into a larger human tragedy."

Earthquakes of similar magnitude claimed more than 200,000 lives in Haiti in January 2010 and 73,000 lives in Kashmir in October 2005.

Foreigners killed 

Those killed included nine Portuguese nationals, five Spaniards, two Brazilians, two Chinese nationals and one Italian-Venezuelan.

Fifty-six Portuguese citizens and 133 Spaniards were missing or otherwise unaccounted for, according to their respective governments.

The quakes were the most powerful since a 7.7-magnitude tremor struck offshore in 1900.

Venezuela's northern coast sits on a boundary between the Caribbean and South American tectonic plates, but has not experienced a major quake since 1997.

This week's twin quakes were felt in neighboring Colombia and northern Brazil.