The 7.7-magnitude quake, one of Myanmar's strongest in a century, jolted the war-torn Southeast Asian nation on Friday, leaving around 1700 people dead, 3400 injured and more than 300 missing as of Sunday, the military government said.
The junta chief, Senior General Min Aung Hlaing, warned the number of fatalities could rise, state media reported, three days after he made a rare call for international assistance.
India, China and Thailand are among Myanmar's neighbours that have sent relief materials and teams, along with aid and personnel from Malaysia, Singapore and Russia.
But residents in the cities of Mandalay and Sagaing reported international aid had not arrived as concerns grew about a severe shortage of food, electricity and water.
"The destruction has been extensive, and humanitarian needs are growing by the hour," the International Federation of Red Cross and Red Crescent Societies said in a statement.
The United States pledged $US2 million ($A3.2 million) in aid "through Myanmar-based humanitarian assistance organisations" and said in a statement that an emergency response team from USAID, which is undergoing massive cuts under the Trump administration, is deploying to Myanmar.
The devastation has piled more misery on Myanmar, already in chaos from a civil war that grew out of a nationwide uprising after a 2021 military coup ousted the elected government of Nobel Peace Prize laureate Aung San Suu Kyi.
The US Geological Survey's predictive modelling estimated Myanmar's death toll could eventually top 10,000 and losses could exceed the country's annual economic output.
Hospitals in parts of central and northwestern Myanmar, including the second-biggest city, Mandalay, and the capital Naypyitaw, were struggling to cope with an influx of injured people, the UN Office for the Coordination of Humanitarian Affairs said late on Saturday.
The Chinese embassy in Myanmar said a Chinese rescue team freed a woman who had been trapped for about 60 hours inside the Great Wall Hotel in Mandalay.
The quake also shook parts of neighbouring Thailand, bringing down an under-construction skyscraper and killing 18 people across the capital, according to Thai authorities.
At least 76 people remained trapped under the debris of the collapsed Bangkok building, where rescue operations continued for a third day, using drones and sniffer dogs to hunt for survivors.
Myanmar's opposition National Unity Government, which includes remnants of the previous administration, said anti-junta militias under its command would pause all offensive military actions for two weeks from Sunday.
In Mandalay, scores of people were feared trapped under collapsed buildings and most could not be reached or pulled out without heavy machinery, two humanitarian workers and two residents said.
"My teams in Mandalay are using work gloves, ropes and basic kits to dig and retrieve people," said one of the humanitarian workers. Reuters is not naming them because of security concerns.
"There are countless trapped and still missing. The death toll is impossible to count at the moment due to the number trapped and unidentified, if alive."
A video filmed by a Mandalay resident on Saturday and shared with Reuters showed patients in beds, some attached to drips, on the grounds outside a 500-bed orthopaedic hospital in the city. Public and private healthcare facilities in Mandalay were damaged by the quake, according to the World Health Organisation.
In Bangkok, at the site of the collapsed 33-storey building, rescuers surrounded by shattered concrete piles and twisted metal continued their efforts to rescue dozens of workers trapped under the rubble.
Teerasak Thongmo, a Thai police commander, said his team of policemen and rescue dogs were racing against time to locate survivors, struggling to move around metal debris and sharp edges on an unstable structure.
"Our team is trying to find anyone that might still be alive. Within the first 72 hours, we have to try and save those still alive," he said.
Near the rescue operations, relatives and friends of the missing and trapped construction workers waited for news. Some broke down.
"Ploy, Ploy, Ploy, my daughter, I'm here for you now!" one woman wailed, as she was hugged by two others.
"Ploy, can you hear me calling out for you?"
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