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BANGKOK 鈥� Thai authorities said Monday they are investigating why a single office tower block under construction in Bangkok collapsed during聽the March 28 earthquake聽that otherwise caused limited damage in the capital.

Bangkok Gov. Chadchart Sittipunt visited the site as workers used heavy equipment to pull away rubble of the 30-story State Audit Office building in hopes of finding the 78 people still missing.

鈥淓ven one life saved is worth all the effort, so I think we have to move on, carry on,鈥� he said.

But building safety is suddenly a concern in the city, where millions of people live and work in thousands of high-rises.

The magnitude 7.7 quake, which was centered more than 800 miles away, killed聽more than 2,000聽people in Myanmar and at least 18 in Thailand, most at the Bangkok construction site near the popular Chatuchak Market.

鈥淚 think we need to find the root cause so at least we can learn some lessons and improve building regulations,鈥� Chadchart said. 鈥淚n the end, we will have some results that will improve safety in Bangkok.鈥�

Shares in the property developer handling the project, Italian Thai Development, fell 27 percent in trading Monday as questions were raised about the building鈥檚 design, enforcement of construction safety codes, and the state-run Chinese contractor building the State Audit Office.

The construction company, a subsidiary of state-run China Railway No. 10 Engineering Group, last year posted a video online celebrating crews topping out the structure at approximately 450 feet. The video included plenty of drone footage and boasted about the quality of the design, construction and project management.

Questions about safety and quality

Interior Minister Anutin Charnvirakul, whose family owns one of Thailand鈥檚 largest construction conglomerates, told reporters he has ordered formation of an investigation committee and for it to report the results to him within seven days. He pointed to three possible factors behind the collapse: the designer, the inspectors or the builders.

鈥淲e will definitely find the true reasons as to why this building has collapsed, because it鈥檚 all scientific,鈥� Anutin said.

While not on a geologic fault, Bangkok is built on relatively unstable alluvial soil, on the banks of the Chao Phraya River. That can amplify ground motion for tall buildings. The city has long been sinking under the weight of its skyscrapers, leading authorities to restrict the use of groundwater to help reduce subsidence.

The recent earthquake gave the Thai capital an unusually long and strong jolt, causing water from rooftop pools to cascade down skyscrapers, light-rail trains to rock on their tracks, and millions of people to flee homes and offices. People waited for hours outside in the blazing midday heat for buildings to undergo safety checks. A warning of aftershocks on Monday caused a brief panic, with some people again heading to the streets.

Questions about enforcement of safety and quality standards in Bangkok were raised earlier by the collapse of parts of a highway under construction in the city鈥檚 outskirts; several construction workers were killed. One potential concern was the quality of the steel rods embedded in concrete slabs and pillars to reinforce them.

Most other damage in the city appeared to be superficial, such as fallen ceiling panels and fittings and cracked plaster. Such damage occurred mainly in relatively newer buildings constructed by private developers.

Revised construction standards

Building owners need to inspect their properties to determine whether any cracks are old or new, Chadchart said. The Thailand Structural Engineers Association was recruiting volunteers to help with inspections. Recently, it urged a review of all large-scale projects in the city.

Most buildings in Bangkok were built before the government revised construction standards to include earthquake safety requirements, said Christian Malaga-Chuquitaype, a lecturer in civil and environmental engineering at the Imperial College in London.

Many structures are built without beams and with 鈥渇lat slabs鈥� and slender columns instead, which maximizes open floor space and minimizes costs, he noted. The company building the State Audit Office boasted in its video that a beamless design was used.

鈥淲hile this design has cost and architectural advantages, it performs poorly during earthquakes, often failing in a brittle and sudden (almost explosive) manner,鈥� he wrote in an analysis. “A thorough forensic analysis is needed, but this building type is no longer recommended in earthquake-prone areas.鈥�

Editor鈥檚 note: Associated Press writers David Rising and Grant Peck contributed to this report.