A strong earthquake rocked Southeast Asia on Friday, bringing down a skyscraper under construction in Bangkok and toppling buildings in neighbouring Myanmar’s second-largest city.

At least one person was killed and dozens of workers rescued from under the rubble of the skyscraper, Thailand's National Institute of Emergency Medicine said.

Witnesses in Bangkok said people ran out onto the streets in panic, many of them hotel guests in bathrobes and swimming costumes as water cascaded down from an elevated pool at a luxury hotel.

The United States Geological Survey (USGS) said the quake, which struck at lunchtime, was of 7.7 magnitude and at a depth of 10 km (6.2 miles). It was followed by a powerful aftershock.

The epicentre was about 17.2 km from the city of Mandalay in Myanmar, which has a population of about 1.5 million.

There was no immediate word from Myanmar authorities on damage.

An officer from the Myanmar Fire Services Department told Reuters: "We have started the search and are going around Yangon to check for casualties and damage. So far, we have no information yet."

Social media posts from Mandalay, Myanmar's ancient royal capital that is at the centre of its Buddhist heartland, showed collapsed buildings and debris strewn across streets of the city. Reuters could not immediately verify the posts.

One witness in the city told Reuters: "We all ran out of the house as everything started shaking. I witnessed a five-storey building collapse in front of my eyes. Everyone in my town is out on the road and no one dares to go back inside buildings."

Another witness in the city, Htet Naing Oo, told Reuters that a tea shop had collapsed with several people trapped inside. "We couldn’t go in," she said. "The situation is very bad."

A third witness said a mosque in the city was badly damaged.

China's Xinhua news agency said strong tremors were felt in southwestern Yunnan province which borders Myanmar, but there were no reports of casualties.

Witnesses contacted in Yangon said many people ran out from buildings in the city, the largest in the country.

One office tower in downtown Bangkok swayed from side to side for at least two minutes, with doors and windows creaking loudly, witnesses said.

Hundreds of employees filed out via emergency stairs as some shocked and panicked workers froze. Loud shrieks could be heard as the building continued to sway.

Outside, hundreds gathered in the afternoon sun, while staff with medical kits found office chairs for elderly and people in shock.