Maneerat Setnawet, the helper of an electrician, was working with her husband on the 23rd floor of a new office tower on the northern limit of Bangkok just before the calamity occurred.

She needed to get some equipment, so she took the construction elevator to the bottom floor. All of a sudden, she felt the ground shiver beneath her and, with two sharp cracking sounds, the unfinished building started to crumble.

With her cellphone in hand, she fled to avoid the falling debris as a huge dust cloud rose. She tried calling her husband, Nugen Setnawet, an electrician, but her calls didn’t go through.

Ever since then, she has remained at the location, quietly observing as rescuers look for survivors. The news has been dismal. Eight bodies were retrieved from the scene on Friday, but only one on Saturday.

“I am still here waiting, waiting for a miracle,” said Ms. Maneerat.

Almost 80 people believed to be in the 30-story building when it collapsed are still unaccounted for.

Rescuers using heavy equipment and search dogs spotted only the one body during the search on Saturday. The pile of rubble — seven stories high — was so unstable that it took hours for them to remove the body.

That brought the total of known fatalities in Bangkok from the quake to 10, including a crane operator who fell to his death from another construction site.

The earthquake’s epicenter was more than 600 miles away to the north near Mandalay, Myanmar’s second-largest city, where the devastation was far more terrible. More than 1,600 deaths have been reported, and the toll is expected to increase significantly.

The search at the site of the crumbled Bangkok building persisted into the night under bright lights. Heavy equipment operators moved significant portions of metal from the debris in the hope of finding survivors.

Hundreds of rescuers from the military, the police, and volunteer organizations helped with the search. Dozens of relatives and friends of the missing workers observed from behind a barrier.

In addition to search dogs, rescue teams utilized thermal sensors to detect those still alive.

Periodically, all activities ceased so searchers could listen for signs of survivors. But by Saturday evening, they had not heard any sounds of assistance from within the heap of debris.

Piyalux Thinkaew, a rescuer from the Ruamkatanyu Foundation, stated that heavy equipment that came on Saturday was being used to remove large pieces of metal and concrete and for workers to carefully avoid destabilizing the mound of debris.

“This is to open a way for us to be able to see underneath and check for any indications of life,” he said. “It’s a very challenging task and risky work for the rescuers as well.”

Suchatvee Suwansawat, a professor of civil engineering at King Mongkut University and a former president of the Council of Engineers Thailand, stated that experts must determine whether the collapse resulted from a design flaw or construction blunder.

An incomplete structure should be no more at risk of collapsing during an earthquake than a completed one, he said.

“It must be 100 percent safe,” he added. There must have been something wrong. It’s like the building exploded. It’s not normal.”

He stated that Thailand had never witnessed the collapse of a structure of this size. To date, he said, two six-story buildings had collapsed, one in 2014 and another in 1993.

“We really have no experience with this,” he said. “We cannot say much yet because we have to examine the coefficients and gather samples and evidence. Everything collapsed at once. And from the video, we saw the columns burst.”

The building was intended to be a government office in Bangkok.

A Chinese state-owned firm, the China Railway 10th Engineering Group, was part of a consortium that won the contract to build the tower, according to an article in People’s Daily, the organ of the Chinese Communist Party, published in 2021. The consortium also included Italian-Thai Development Plc, based in Bangkok.

Neither organization could be immediately contacted for comment.

The project, which started in April 2021, was one of the tallest structures China Railway 10th Engineering Group had built, according to People’s Daily at the time.

The company is a subsidiary of China Railway Group, a state-owned giant heavily involved in China’s Belt and Road Initiative, a global infrastructure project aimed at expanding the country’s supply chain networks and influence.

Saifon Thongsuk, 36, was among those waiting at the site for information about missing relatives, including her aunt, uncle, and two adult children, all working on the office tower.

They had been working at a different construction site on the outskirts of Bangkok but were recently sent to the site because of an urgent need for workers, she said.

“I don’t know how long they had been working here,” she said. “I only know they were working on the top floor.”

Naruemol Thonglek, 44, came to the site looking for six people, including her husband, his son, and four co-workers.

Ms. Naruemol had been working at the site as well, but stopped because her husband was concerned that it was exhausting her.

“I rushed here as soon as I heard about the earthquake,” she said. “I tried to contact him. Messages were not delivered. Calls were not going through. I can’t reach any of them.”

She continued, “I guess he is in the middle of that pile of rubble. Maybe there is some space for air, I don’t know. I can only hope for a miracle.”

Thurian Pheungrod, 47, also came to the site on Friday after hearing that his brother and sister-in-law were trapped in the collapsed building. They had been working at the site for several months.

“I initially still believed that a miracle could happen,” he said. “I still had hope. But I no longer hope for a miracle.”