Residents scrambled desperately through collapsed buildings Sunday searching for survivors as aftershocks rattled the devastated city of Mandalay, two days after a massive earthquake killed more than 1,600 people in Myanmar and at least 11 in neighboring Thailand. 

The initial 7.7-magnitude quake struck near the central Myanmar city of Mandalay early Friday afternoon, followed minutes later by a 6.7-magnitude aftershock.

The tremors collapsed buildings, downed bridges and buckled roads, with mass destruction seen in the city of more than 1.7 million people.

As dawn broke Sunday, tea shop owner Win Lwin picked his way through the remains of a collapsed restaurant on a main road in his neighborhood, tossing bricks aside one by one.

"About seven people died here" when the quake struck Friday, he told AFP. "I'm looking for more bodies but I know there cannot be any survivors.

"We don't know how many bodies there could be but we are looking."

About an hour later, a small aftershock struck, sending people scurrying out of a hotel for safety, following a similar tremor felt late Saturday evening.

Truckloads of firemen gathered at one of Mandalay's main fire stations to be dispatched to sites around the city.

The night before, rescuers had pulled a woman out alive from the wreckage of a collapsed apartment building, with applause ringing out as she was carried by stretcher to an ambulance.

Myanmar's ruling junta said in a statement Saturday that at least 1,644 people were killed and more than 3,400 injured in the country, with at least 139 more missing.

But with unreliable communications, the true scale of the disaster remains unclear in the isolated military-ruled state, and the toll is expected to rise significantly.

Junta chief Min Aung Hlaing issued an exceptionally rare appeal for international aid on Friday, indicating the severity of the calamity. 

Previous military governments have shunned foreign assistance, even after major natural disasters.

Myanmar has already been ravaged by four years of civil war sparked by a military coup in 2021.

Anti-junta fighters in the country have declared a two-week partial ceasefire in quake-affected regions starting Sunday, the shadow "National Unity Government" said in a statement.

The government in exile said it would "collaborate with the UN and NGOs to ensure security, transportation, and the establishment of temporary rescue and medical camps" in areas that it controls, according to the statement, which was released on social media.

Aid agencies have warned that Myanmar is unprepared to deal with a disaster of this magnitude.

Some 3.5 million people were displaced by the raging civil war, many at risk of hunger, even before the quake struck.

Bangkok building collapse

Across the border in Thailand, rescuers in Bangkok worked Sunday to pluck out survivors trapped when a 30-storey skyscraper under construction collapsed after the Friday earthquake.

At least 11 people have been killed in the Thai capital, with dozens more still trapped under the immense pile of debris where the skyscraper once stood.

Bangkok authorities were expected to release another statement at 9 am (0200 GMT), with fears of a further toll increase.

Workers at the site used large mechanical diggers in an attempt to find victims still trapped on Sunday morning.

Sniffer dogs and thermal imaging drones have also been deployed to seek signs of life in the collapsed building, close to the Chatuchak weekend market popular among tourists.

Authorities said they would be deploying engineers to assess and repair 165 damaged buildings in the city on Sunday.