"Infrastructure such as roads, bridges, and buildings were affected, leading to casualties and injuries among civilians. Search and rescue operations are currently being carried out in the affected areas," the military government said in a statement issued on state media.
The junta leader, General Min Aung Hlaing, warned of more deaths and injuries as he invited "any country" to provide help and donations.
The United States Geological Service's predictive modelling estimated the death toll could exceed 10,000 people in Myanmar, and that losses could be greater than the value of the country's gross domestic product.
Much of the devastation was in Myanmar's second-largest city, Mandalay, which lies close to the epicentre of the 7.7 magnitude quake that struck at lunchtime and was followed by a powerful aftershock and several more moderate ones.
In the Thai capital Bangkok, 1000km from the epicentre a rescue mission was stepped up on Saturday to find construction workers trapped under the rubble of a collapsed 33-storey tower.
A 37-strong team from China landed in Yangon, Myanmar's former capital, early on Saturday, carrying medicine and equipment to detect signs of life with them, the Chinese embassy said in a Facebook post.
Russia said it was sending 120 experienced rescuers as well as doctors and search dogs, state news agency TASS reported.
Speaking at the White House later on Friday, US President Donald Trump said he had spoken with officials in Myanmar and his administration would be providing some form of assistance.
"We're going to be helping," he told reporters.
In the Thai capital Bangkok, an official said at least nine people had been killed. Rescuers were searching through the rubble of the tower block that collapsed.
Mandalay, with a population of about 1.5 million, is Myanmar's ancient royal capital and the centre of its Buddhist heartland. Rescue workers were trying to reach dozens of monks trapped under rubble in the Phaya Taung Monastery, said the emergency worker in Amarapura. Buildings, bridges and roads were wrecked, residents and local media said.
"We all ran out of the house as everything started shaking," a Mandalay resident 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."
A rescue worker from the Moe Saydanar charity told Reuters it had retrieved at least 60 bodies from monasteries and buildings in Pyinmana, near the capital Naypyidaw, and more people were trapped.
In the purpose-built capital itself, a 1000-bed hospital sustained damage and roads were left with huge fissures, state media reported.
UN Secretary-General Antonio Guterres said the United Nations was mobilising in Southeast Asia to help those in need.
Zin Mar Aung, the diplomatic spokesperson for the opposition National Unity Government, said fighters from the anti-junta militias known as the People's Defence Forces would provide humanitarian help.
State media said 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. Images showed the destroyed Ava Bridge over the Irrawaddy River, its arches leaning into the water.
At least three people died after a mosque in Taungoo partially collapsed, two witnesses said.
"We were saying prayers when the shaking started... Three died on the spot," one person said.
Local media reported a hotel in Aung Ban, in Shan state, crumbled into rubble, with the Democratic Voice of Burma reporting two people had died and 20 were trapped.
Amnesty International said the earthquake could not have come at a worse time for Myanmar, given the number of displaced people, the existing need for relief aid, and cuts to US aid by the Trump administration.
Of the confirmed casualties in the Thai capital, eight died in the building collapse and a ninth at another location, Bangkok Deputy Governor Tavida Kamolvej said. The rescue operation at the building site said over 100 people were missing.
