The 7.7-magnitude quake, one of Myanmar's strongest in a century, jolted the war-torn Southeast Asian nation on Friday, leaving about 1700 people dead, 3400 injured and more than 300 missing as of Sunday, the military government said.
Junta chief Senior General Min Aung Hlaing warned the number of fatalities could rise and his administration faced a challenging situation, state media reported, three days after he made a rare call for international assistance.
Neighbouring India, China and Thailand have sent relief materials and teams, along with aid and personnel from Malaysia, Singapore and Russia.
"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.
"With temperatures rising and the monsoon season approaching in just weeks, there is an urgent need to stabilise affected communities before secondary crises emerge."
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.
Critical infrastructure - including bridges, highways, airports and railways - across the country of 55 million lay damaged, slowing humanitarian efforts while a civil war that has battered the economy, displaced more than 3.5 million people and debilitated the health system rages on.
The US Geological Service's predictive modelling estimated Myanmar's death toll could top 10,000 and losses could exceed the country's annual economic output.
Hospitals in parts of central and northwest 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 Co-ordination of Humanitarian Affairs said late on Saturday.
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 building, where rescue operations continued for a third day, using drones and sniffer dogs to hunt for survivors.
The 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.
Sections of a major bridge connecting Sagaing to nearby Mandalay collapsed, satellite imagery showed, with spans of the colonial-era structure submerged in the Irrawaddy river.
"With bridges destroyed, even aid from Mandalay is struggling to get through," Sagaing Federal Unit Hluttaw, a political association linked to the NUG, said on Facebook.
"Food and medicine are unavailable, and the rising number of casualties is overwhelming the small local hospital, which lacks the capacity to treat all the patients."
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," one of the humanitarian workers said.Â
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.
Public and private health care facilities in Mandalay, including the Mandalay General Hospital and parts of Mandalay Medical University, were damaged by the quake, according to the World Health Organization.
Russian and Indian rescue workers were heading to Mandalay, and multiple teams of Chinese, Thai and Singapore rescue personnel have also arrived.
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.
"Right now, our team is trying to find anyone that might still be alive," he said.
