March 28 (Reuters) - A powerful earthquake rocked Southeast Asia on Friday, killing several people, bringing down a skyscraper under construction in Bangkok and toppling buildings and bridges in neighbouring Myanmar, where the ruling junta declared a state of emergency in some areas.

At least three people were killed in the town of Taungoo in Myanmar when a mosque partially collapsed, witnesses said, while local media reported that at least two people died and 20 were injured after a hotel collapsed in Aung Ban.

In Thailand, Bangkok Governor Chadchart Sittipunt said there had been three deaths from the quake. He warned of possible aftershocks but urged people to be calm and said the situation was largely under control.

At least one person was killed and dozens of workers were rescued from under the rubble of the skyscraper that had been under construction in Bangkok, Thailand's National Institute of Emergency Medicine said.

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

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

The quake was followed by a powerful aftershock and several more moderate ones.

In Myanmar, the quake caused the collapse of buildings in five cities and towns, as well as a railway bridge and a road bridge on the Yangon-Mandalay Expressway, state media said.

"We all ran out of the house as everything started shaking," a resident in Mandalay told Reuters. "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."

Myanmar's ruling military declared a state of emergency in multiple regions.

"The state will make inquiries on the situation quickly and conduct rescue operations along with providing humanitarian aid," it said on the Telegram messaging app.

The junta seized power in a 2021 coup that led to a civil war, and has been isolated internationally.

Mandalay is Myanmar's ancient royal capital and at the centre of the country's Buddhist heartland.

Social media posts showed collapsed buildings and debris strewn across streets in the city. Reuters could not immediately verify the posts.

Local media outlet Myanmar Now posted images showing a clock tower had collapsed and part of the wall by Mandalay Palace was in ruins.A 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."

At least three people died after a mosque in Taungoo partially collapsed, two eyewitnesses told Reuters.

"We were saying prayers when the shaking started... Three died on the spot," said one of two people who spoke to Reuters.

Local media reported a hotel in Aung Ban, in Shan state, crumbled into rubble, with one outlet, the Democratic Voice of Burma, reporting two people had died and 20 were trapped.

Video and images posted by Myanmar Now showed a roof cratered at a market in the capital, Naypyitaw.Witnesses contacted in Yangon, Myanmar's largest city, said many people ran out of buildings.

OFFICE TOWER SHAKES IN BANGKOK

The Stock Exchange of Thailand suspended all trading activities for the Friday afternoon session.

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.

"At first, I didn?t realise (it was an earthquake)," office worker on Varunyou Armarttayakul told Reuters. "But then I saw the table shaking, and the chair and computer started swaying, too. I only knew for sure when I heard the noise of the cracking walls and cracking glass. Part of the ceiling even collapsed ? that?s when I had to run out.? Outside, hundreds gathered in the afternoon sun, while staff with medical kits found office chairs for the elderly and people in shock.

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

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