LA GUAIRA : Rescue crews raced Saturday to find survivors in the rubble of Venezuela's powerful earthquakes as the death toll reached 1,430 and hopes dwindled 72 hours after the earth roared and rumbled.

Millions of people were feared to lack sanitation and other basic needs, as the first US aid flights landed in Caracas.

Tens of thousands of people were reported missing as collapsed buildings dotted cities in a country already enduring an economic crisis and political upheaval after US special forces captured authoritarian leader Nicolas Maduro in January.

Facing public outrage at the response by local officials, Venezuela's US-backed interim leader Delcy Rodriguez thanked other countries for the outpouring of aid.

The search for survivors saw desperate attempts by local residents to claw away rubble from buildings that collapsed in Wednesday's two quakes.

Experts say the first 72 hours after natural disasters are the key, narrow window for finding the living. After that the search becomes one of recovering bodies.

"It's just very chaotic, hot and unorganized," said Australian firefighter Craig Demeillon, 43, who traveled alone to La Guaira from Miami to help. "Hopefully there's more people to find."

A Salvadoran rescue worker who declined to give his name put it this way: "At this point, they are probably dead bodies. Thanks to God maybe we can find people still alive."

UN aid chief Tom Fletcher on Friday told AFP the death toll could continue to soar, adding that more than 50,000 people were missing.

The United States said one runway at Simon Bolivar International Airport was partially functioning to receive C-17 US military planes, while a naval ship had arrived off the coast.

- Newborn rescued -

There was joy in the hardest-hit coastal area of La Guaira, north of Caracas, when locals pulled an infant alive out of the wreckage on Friday, some 32 hours after the magnitude 7.2 and 7.5 tremors.

In one social media video, a man welled up in tears as he held the baby in his arms.

The UN migration agency said it had examined available population and damage data and had determined that "up to 6.76 million people could be affected," and would "require emergency shelter, safe water, sanitation and hygiene services, healthcare, protection support and essential relief items."

National Assembly President Jorge Rodriguez reported on Saturday 1,430 dead and 3,238 people injured, while the UN estimated $6.7 billion in physical damage -- equivalent to six percent of Venezuela's GDP.

- 'Permit to save lives' -

Venezuelans -- already battered by years of a failing economy and the turbulence of the US intervention to topple Maduro in January -- were furious at the government.

Yessica Mendoza was forced to transport her own daughter to a morgue in Caracas after 25-year-old Yesimar Rodriguez and her husband Jhomel Anaya, 26, did not survive the tumbling debris of their home in La Guaira on Wednesday.

"We were the ones who pulled them out ourselves. No help ever came," the bereaved mother, 43, told AFP, adding that the couple would be cremated without a wake due to the rapidly advancing decomposition of their bodies.

The government has restricted access to La Guaira state, deployed the military to the area and made it obligatory for volunteers to obtain a safe-entry pass.

Anger among those impatiently waiting to volunteer surged as they waited for passes outside a concert hall in the capital.

"You need a permit to save lives -- just imagine," complained Carlos Itriago, 27.

"I've been here since dawn standing in line so I can go rescue people," said Ezequiel Rivero, 53.

"Look at what time it is... how many lives have we already lost by now?"

- Venezuela already in trouble -

Rodriguez said she had spoken with US President Donald Trump and Secretary of State Marco Rubio, who "reaffirmed their commitment to supporting the response efforts."

The US said earlier it was sending a disaster response team of more than 250 personnel, including three special search-and-rescue units with dogs trained to locate people trapped beneath the rubble.

Twenty-one countries were sending search-and-rescue teams, parliament chief Rodriguez said.

Venezuela's worst earthquakes in more than a century have come after the oil-rich country endured more than a decade of economic collapse.

The crisis has hollowed out hospitals and public services, driving millions to leave the country.

And the country remains in a fragile political transition six months after the US ouster of Maduro.

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

Those killed in Venezuela included 28 Portuguese nationals, five Spaniards, two Brazilians, seven Chinese nationals, one Chilean, one Italian-Venezuelan and one Uruguayan.