A powerful earthquake hit Myanmar and neighboring Thailand on Friday, turning a major hospital in the Myanmar capital into a "mass casualty area" and trapping dozens of workers in an under-construction skyscraper in Bangkok.

The 7.7-magnitude tremor hit northwest of the city of Sagaing on Friday afternoon at a shallow depth, the United States Geological Survey said. A 6.4-magnitude aftershock hit the same area minutes later.

The quakes wrought widespread damage, particularly in Myanmar, where buildings fell onto their sides, roads cracked open, and the well-known Ava bridge collapsed near the epicenter.

In the capital Naypyidaw, AFP journalists saw the entrance of the emergency department at the city's main hospital pancaked onto a car.

Wounded at the 1,000-bed facility were being treated outside, intravenous drips hanging from their gurneys. Some writhed in pain, others lay still as relatives sought to comfort them.

A hospital official ushered journalists away, saying: "this is a mass casualty area."

Another official said hundreds of injured people had arrived at the facility.

"I haven't seen (something) like this before. We are trying to handle the situation. I'm so exhausted now," a doctor told AFP.

The route to the hospital was jammed with vehicles. An ambulance tried to make its way through, a paramedic shouting "cars, move aside so the ambulance can get through."

At the city's National Museum, pieces fell from the ceiling as the building began shaking. Uniformed staff ran outside, some trembling and tearful, others grabbing cellphones to try to contact loved ones. 

Skyscraper collapse

Across the border in Thailand, where strong quakes are rare, the powerful tremors sent residents across many cities flooding out into the streets in panic.

In Bangkok, a 30-story building under construction collapsed, trapping 43 workers, police and medics said.

The massive building intended for government offices was reduced to a tangle of rubble and twisted metal in seconds, footage shared on social media showed.

An AFP photographer at the site saw ambulances and rescue teams at the site, near the city's sprawling Chatuchak market, a popular destination for tourists and locals alike.

"When I arrived to inspect the site, I heard people calling for help, saying help me," Worapat Sukthai, deputy police chief of Bang Sue district, told AFP.

"We estimate that hundreds of people are injured but we are still determining the number of casualties," he said.

Across Bangkok and the northern tourist destination of Chiang Mai, where the power briefly went out, stunned locals rushed outside, unsure of how to respond to the unusual quake.

Sai, 76 was working at a minimart in the northern city when the shop started the shake.

"I quickly rushed out of the shop along with other customers," he said.

"This is the strongest tremor I've experienced in my life."

Buildings damaged

The quake prompted Thai Prime Minister Paetongtarn Shinawatra to declare a state of emergency in Bangkok, where some metro and light rail services were suspended, further snarling the city's already notorious traffic.

Airports were operating as normal.

Earlier, the prime minister said she had interrupted an official visit to the southern island of Phuket to hold an "urgent meeting" after the quake, according to a post on X.

The quake was felt across the region, with China, Cambodia, Bangladesh and India all reporting tremors.

A livestream broadcast by the state-linked Beijing News showed around a dozen emergency workers in orange jumpsuits and helmets standing behind a cordon on a street strewn with fallen masonry in the city of Ruili, on the Chinese border with Myanmar.

A female shop worker interviewed on the livestream showed phone footage of people running out of stores with their hands over their heads as tremors swept through the street, only to rush back inside when what was described as a nearby burst pipe drenched them with water from above.

A video posted on Douyin, the Chinese version of TikTok, and geolocated by AFP showed a torrent of water and debris cascading from the roof of a high-rise block in Ruili as people fled through a street market below.

India's Prime Minister Narendra Modi said his country was ready to offer "all possible assistance" to Myanmar and Thailand and had placed authorities on standby for requests.

Earthquakes are relatively common in Myanmar, where six strong quakes of 7.0 magnitude or more struck between 1930 and 1956 near the Sagaing Fault, which runs north to south through the center of the country, according to the USGS.

A powerful 6.8-magnitude earthquake in the ancient capital Bagan in central Myanmar killed three people in 2016, also toppling spires and crumbling temple walls at the tourist destination.

by Sebastien Berger and Hla Hla Htay with Thanaporn Promyamyai in Bangkok and Montira Rungjirajittranon in Chiang Mai