A 7.7-magnitude earthquake struck central Myanmar on Friday, sending shock waves across Southeast Asia and causing deaths and damage hundreds of miles away from the epicenter.

The International Rescue Committee says at least 80 people are reported to have died in Myanmar. The death toll there is expected to rise, with many injured arriving at hospitals in the country’s second-largest city, Mandalay.

The earthquake collapsed a skyscraper under construction in Bangkok, leaving at least three people dead and dozens missing. It also shook buildings in China and rattled bridges and homes as far away as Vietnam.

Myanmar is in the throes of a civil war that has left nearly 20 million people without proper food and shelter. Censorship imposed by Myanmar’s military government has limited the spread of information from the heart of the disaster, even as the scale of damage in Thailand and other countries is slowly becoming clear.

Where was the epicenter?

The quake struck near Mandalay, in central Myanmar, at roughly 12:50 p.m. local time, according to the U.S. Geological Survey. Approximately 12 minutes later, an aftershock with a magnitude of 6.4 hit the same area.

An earthquake with a magnitude of 7.7 is considered major. The magnitude of the aftershock is categorized as strong and likely to cause damage, particularly in densely populated areas, according to the agency.

Central Myanmar, where large plates of the Earth’s crust are in motion, is prone to powerful earthquakes. The country lies on the eastern end of the Alpide Belt, one world’s most active zones of seismic activity. Three quakes of magnitude 7.7 or greater have struck in or near Myanmar in the last century, according to a U.S.G.S. database, with the most recent in 1988.

The earthquake on Friday struck at a relatively shallow depth of six miles, meaning it was likely to cause more violent shaking. That shaking was felt as far away as Thailand’s capital, Bangkok, more than 800 miles away from the epicenter.

Which countries have been affected?

Despite the limited information from the authorities in Myanmar, the earthquake was almost certainly most destructive there. The city of Mandalay, the largest major city near the epicenter, has an estimated population of 1.5 million people.

Neighboring Thailand also felt the might of the earthquake, particularly in Bangkok, where around 11 million people live in the metropolitan area. Prime Minister Paetongtarn Shinawatra declared the city an “area of emergency,” asking residents to evacuate from tall buildings to avoid aftershocks.

In China, news media outlets in Yunnan Province, neighboring Myanmar, reported damage to buildings in the busy border city of Ruili.

The shaking was also felt in Bangladesh, to Myanmar’s west, but there were no immediate reports of damage.

What is the death toll, and what damage has been caused?

The toll is expected to rise as rescue workers dig through the rubble and injured people make their way to hospitals. In Myanmar, at least 20 people were reported dead, and another 300 were injured, according to a doctor at the Mandalay General Hospital.

In Mandalay, video showed that the Ava Bridge, originally built by the British in the 1930s, had partly collapsed, according to footage verified by The New York Times. But heavy censorship enforced by Myanmar’s military government has made it hard to see the full extent of the damage.

In Thailand, at least three people died when a skyscraper that had been under construction collapsed in Bangkok. At least 70 people were still missing, while it was unclear whether another 20 people who trapped in an elevator shaft were still alive. The city’s elevated train service was shut down and people fled from tall buildings after the city was placed in a state of emergency.

Chinese state media reported that an unspecified number of people were injured, with houses and buildings damaged in the city of Ruili.

What aid is available?

In Myanmar, the areas worst hit are in the center of the country, which are controlled by the military junta. When disasters have struck the past, like Cyclone Mocha in 2023 and Cyclone Nargis in 2008, the military government avoided asking for international assistance and throttled aid in areas not under its control.

In the wake of the powerful earthquake that struck on Friday, the junta made a rare appeal for help. The plea signaled that the authorities are bracing for a high death toll.

“We will cooperate with them to ensure the best care for the victims,” said Gen. Zaw Min Tun, Myanmar’s military spokesman, after the government declared a state of emergency in six regions.

Areas of the country that are controlled by rebel forces are farther from the epicenter of the quake. These areas appear to be relatively unscathed, but information in these often isolated areas may be slow to emerge.

The World Health Organization said it is looking at sending trauma supplies to support Myanmar. The International Federation of Red Cross and Red Crescent Societies said teams in the country were assessing the situation.

Reporting was contributed by Sui-Lee Wee, John Yoon, Keith Bradsher, John Keefe, Richard C. Paddock, Muktita Suhartono, Adam Satariano and Paul Mozur.