A powerful 7.7 magnitude earthquake rattled much of Southeast Asia on Friday, resulting in mounting casualties and flattened skyscrapers from Myanmar to Thailand. The epicenter was in Mandalay, Myanmar, the country's second-largest city. Even Bangkok, some 600 miles away, felt widespread shaking and saw significant damage from the quake -- including the total collapse of a skyscraper under construction. Casualties are expected to rise as search and rescue efforts are underway in collapsed buildings in Myanmar and Thailand, officials said. At least 1,644 people were killed in Myanmar, according to the latest official death toll cited by the state-run MRTV broadcaster. Another 3,408 people were injured and 130 others were still missing. In Bangkok, at least 18 people were killed, including 11 who were killed in a building collapse in Chatuchak, according to the Bangkok Metropolitan Administration. Thirty-three others were injured and another 78 were missing in Bangkok, the Royal Thai Police said. A 5.1 magnitude earthquake struck about 17 miles north of Mandalay, Myanmar, on Sunday afternoon, according to the U.S. Geological Survey. The quake near the second-largest city in Myanmar came amid a series of aftershocks following a powerful 7.7 magnitude that struck the country with an epicenter near Mandalay on Friday afternoon. Myanmar resistance group announces partial ceasefire Myanmar's National Unity Government has announced it will implement a "two-week pause in offensive military operations" in areas affected by the earthquake starting March 30. The National Unity Government is the representative body of the ousted civilian government that was overthrown in the 2021 military coup, which led to the ongoing civil war. The military government in Myanmar has not made a similar announcement. American couple talks about surviving quake Garret Briere and his wife told ABC News they never could have imagined that their first vacation to Thailand ended up being one of the most terrifying experiences of their lives. The couple from Washington state were in the mall across the street from the 34-story building when they saw it implode and crash to the ground. "We ran out of the building because it started shaking," Garret said. "I grabbed my wife’s hand and I said, 'Don’t let go.' Immediately, we were just covered in dust and debris, and we couldn’t see, and there were thousands of people just in a panic." It took just several seconds for the entire building to be reduced to a 7-story high pile of rubble, the couple said. -ABC News' Brit Clennett, Karson Yiu, Gamay Palacios and Preechaya Rassadanukul Death toll rises to 1,002 in Myanmar, 9 in Thailand The death toll in Thailand from Friday’s earthquake has increased to nine, according to the country’s Department of Disaster Prevention and Mitigation. Another 1,002 have died in Myanmar. Another nine people remain injured and 101 others are still missing. The earthquake and its aftershocks caused damage across 13 Thai provinces as well as in Bangkok, the agency said. A 30-story building that was under construction collapsed in the Thai capital on Friday when the powerful quake struck the region. Search and rescue efforts were ongoing at the scene, with crews detecting 15 signs of life beneath the rubble on Saturday, according to Thailand’s National Institute of Emergency Medicine. Rubio says US willing to help, but not actively assisting yet Secretary of State Marco Rubio posted about the potential U.S. response to the earthquake, and seemed to suggest the president meant the U.S. was willing to help rather than actively assisting. "My prayers go out to the people of Burma and Thailand who are impacted by the earthquake," he wrote. "We've been in contact with these countries and, as @POTUS said, stand ready to provide assistance." Rubio also confirmed the State Department’s teams in the impacted countries were safe and accounted for. The U.S. Embassy in Myanmar has suspended nonemergency consular services for the time being. The U.S. mission to Thailand has not reported any disruption in services. State Department 'evaluating the need' for earthquake response State Department spokesperson Tammy Bruce said despite the tumult at the U.S. Agency for International Development, the U.S. has maintained "a team of disaster experts with the capacity to respond if disaster strikes," which are commonly referred to as DART teams. "These expert teams provide immediate assistance, including food and safe drinking water needed aftermath of a disaster. The United States is evaluating the need for assistance based on requests and dynamic reporting,” she said. But despite President Donald Trump's assertion that the U.S. is going to be helping, Bruce suggested the State Department was still in standby mode. "What I can tell you is that we wait for formal requests," she said. "We are ready. Obviously, we are watching what is transpiring." Bruce insisted that despite the funding flip-flops and reorganization of USAID, "there has been no impact on our ability to perform those duties, those requests for aid, if and when they come in." American recounts being stranded after earthquake An American who was on a subway train in Bangkok when the earthquake struck recounted being stranded as transportation in the city ground to a halt. When her train stopped, Sid Simone said she went on Facebook to find out what was going on. "I saw 'earthquake in Bangkok,' and so at that point, I knew that the entire city was going to start to diminish," the Michigan native told ABC Grand Rapids affiliate WZZM in an interview earlier Friday. "I have been trying to get home for five hours now." With no train service, Simone, who is in Bangkok to make a documentary on vegan food, said she got into a taxi but abandoned it when traffic came to a standstill and the vehicle was low on gas. WZZM spoke to her as she was walking along a highway, still about an hour from home. "It's unfortunate because there's so many people that, we're all fighting trying to get home, but some people are trying to fight to get home because their family member is under that building, you know. Somebody didn't make it home," she told WZZM. She told the station that her apartment complex was just down the street from where the under-construction high-rise collapsed. "I was so blessed that I was not there today," she said. “I could have been shopping in that area." Trump: 'We're going to be helping' Asked about the Myanmar earthquake during a press event at the White House, U.S. President Donald Trump said, "We're going to be helping." "It's terrible what's happened," he said. "We've already spoken with the country." Trump did not elaborate on how the U.S. plans to send foreign aid. Scene in Bangkok was ‘pretty insane,' eyewitness says Michelle Moody, an American living in Bangkok, was on her way to lunch with friends when the earthquake occurred. "It was pretty insane," she told ABC News Live. "I lived in D.C. in 2011 with the earthquake there, and being an American, I had an idea of what to do, but most people were just running around kind of crazy and just trying to escape buildings so as quick as they possibly could." In the aftermath of the quake, people were assessing damage to their residences and, with trains shut down, walking home, she said. Aftershocks remain a concern. "I live in a high-rise, so definitely fear of aftershocks are something I'm worried about," she said. Witness captures Bangkok building collapse while driving on highway Jack Brown was driving on a highway in Bangkok and thought he had punctured a tire when his vehicle swerved a little bit. "I parked the car in stationary and realized that the car was still moving around quite a lot and I immediately knew then it was an earthquake," Brown told ABC News Live. Concerned about being on the elevated highway during the earthquake, he continued along and saw a building under construction collapse "in a matter of seconds." He captured the collapse on video from his car. "It was just horrifying to see that destruction, knowing that there are very likely a lot of people in the site," he said. At least eight people were killed in the collapse, as a search and rescue effort is underway for more than 100 who remain missing, police said. Brown said he had never experienced anything like this in his 10 years of living in Bangkok. "When you're in an earthquake, you don't know if you're at the beginning of it, the middle or the end. Are there going to be any other aftershocks or any other earthquakes following this one? Are they going to get worse?" he said. "There was concern, but it was unprecedented for me, I didn't really know what to expect or what to do, and I just wanted to sort of keep moving and get away from that zone." 8 dead in skyscraper collapse in Bangkok At least eight people were killed and nine injured when a skyscraper that was under construction collapsed in Bangkok, according to the Royal Thai Police. A search and rescue effort is continuing into the night for those who remain trapped, with more than 100 people still missing, police said Officials said earlier there were approximately 320 construction workers on site when the building in Bangkok collapsed.