Content Warning: earthquake aftermath

The following report contains details about a devastating earthquake that resulted in loss of life, building collapses, and ongoing rescue operations in Myanmar and Thailand. Some descriptions may be distressing. Reader discretion is advised.

A powerful earthquake killed more than 20 people across Myanmar and Thailand on Friday, toppling buildings and bridges and trapping over 80 workers in an under-construction skyscraper in Bangkok.

The shallow 7.7-magnitude tremor hit northwest of the city of Sagaing in central Myanmar, and was followed minutes later by a 6.4-magnitude aftershock.

The quake's devastation prompted a rare request for international aid from Myanmar's isolated military junta, which has lost swathes of territory to armed groups. A state of emergency was declared across the six worst-affected regions.

"About 20 people" were confirmed dead at a hospital in Naypyidaw, a doctor told AFP on condition of anonymity.

Across the border in Thailand, three people were confirmed dead in the collapse of a skyscraper, with 81 more missing and believed trapped in the twisted metal and rubble of the under-construction building.

Myanmar looked to have borne the brunt of the quake, with hundreds of casualties flooding a hospital in the capital Naypyidaw. The emergency department's entrance had collapsed onto a car, with medics treating patients outside.

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

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

AFP reporters saw junta chief Min Aung Hlaing arrive at the hospital as the ruling military called for foreign help.

"We want the international community to give humanitarian aid as soon as possible," junta spokesman Zaw Min Tun told AFP at the hospital.

The rare plea from the junta raises the prospect that damage and casualties may be on a large scale, with Myanmar's medical system and infrastructure ravaged by four years of civil war.

Skyscraper collapse

In Thailand, Deputy Prime Minister Phumtham Wechayachai told reporters at least three workers had been killed, with 81 more trapped, after the collapse of a building under construction near the sprawling Chatuchak market.

Rescuers were surveying the tangle of rubble and twisted metal for a safe way to search for survivors, an AFP photographer at the scene said.

"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," he said.

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

"I quickly rushed out of the shop along with other customers," said Sai, 76, who was working at a minimart in Chiang Mai when the shop started to shake.

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

Buildings damaged

Thai Prime Minister Paetongtarn Shinawatra declared an emergency zone in Bangkok, where some metro and light rail services were suspended, further snarling the city's already notorious traffic.

The streets of the capital were full of commuters attempting to walk home, or simply taking refuge in the entrances of malls and office buildings.

City authorities said parks would stay open overnight for those unable to sleep at home.

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

India, France and the European Union all offered to provide assistance.

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

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.

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 United States Geological Survey (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.