Tremors were felt as far away as Bangkok, almost 800 kilometres from the epicentre, Hanoi and parts of China when the earthquake hit late on Thursday, which the US Geological Survey (USGS) measured at magnitude 6.8.
A Myanmar official said 74 people were killed and 110 were injured in five areas close to the epicentre. More than 240 buildings had collapsed.
"We are trying to reach the remote areas," the official said.
"The military, police and local authorities are trying to find some people injured in those affected areas but the roads are still closed."
Across the border, Thai authorities said a 52-year-old woman was killed in Mae Sai district after a wall in her house collapsed.
Terrified residents across the region fled their homes, tall buildings swayed and hospitals and schools were evacuated.
In Yangon Chris Herink, Myanmar country director for the charity World Vision, said there did not appear to be "catastrophic infrastructure damage" in the affected areas of Kengtung and Tachileik, although buildings were cracked and water supplies disrupted in some parts.
"Of real concern though are the more rural areas. There will be more, I am afraid to say, unhappy information coming throughout the day," he said.
"It is a hilly area near the border between Thailand and Laos, the so-called Golden Triangle. There is a lot of commerce that goes on in the area."
World Vision helps care for around 7,000 children sponsored by overseas donors in the affected areas.
"We want to ensure that they and their families are safe, secure and accounted for and to offer assistance to them as a first priority but also to help anyone in the area that has humanitarian needs," he said.
The quake struck 90 kilometres (60 miles) north of Chiang Rai and 235 kilometres (150 miles) north-northeast of Chiang Mai, Thailand's second city and a popular tourist destination.
Thailand's meteorological department on Friday said it had registered six large aftershocks following the initial quake.
Residents in Chiang Rai city raced from their homes again on Friday morning as a large tremor again shook the ground.
Four pagodas in the historic town of Chiang Saen near the northern Thai border were damaged, including Chedi Luang, where its three-metre (10-foot) long pinnacle crashed to the ground.
The shaking was felt throughout China's southwestern province of Yunnan, according to state-run China National Radio, but no casualties or major structural damage had been reported as of Friday morning.
However, the earthquake reportedly caused cracks in some homes and schools in and around the rugged Xishuangbanna region that borders Myanmar, and fear of aftershocks forced many people in the area to spend the night outdoors.
Some residents of the Vietnamese capital Hanoi fled their homes when the quake shook the city.
Le Huy Minh, assistant director of the national Global Geophysics Institute in the capital, reported no victims or damage.
"There was big panic among the local residents," as high buildings shook for half a minute, said Nguyen Thai Son, of the institute's office in northwestern Dien Bien town, 350 kilometres from the epicentre.
But he added there were "neither victims nor material losses here".
Laos government spokesman Khenthong Nuanthasing said there had been no reports of casualties in his country from the earthquake.
"In Vientiane it was not strong," he said.
The quake comes two weeks after Japan was hit by a monster earthquake and tsunami that left around 27,000 people dead or missing and triggered a crisis at its Fukushima nuclear plant.
Myanmar and Japan sit on different tectonic plates, separated by the vast Eurasian plate.
No tsunami warning was issued after the Myanmar quake as US seismologists said it was too far inland to generate a devastating wave in the Indian Ocean.
The USGS initially recorded the quake as magnitude 7.0, but later revised it down to 6.8.
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