NAYPYIDAW, Myanmar: A powerful earthquake hit Myanmar and neighbouring 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 epicentre.

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