Only one building in Bangkok fell during the earthquake on Friday that rocked Myanmar, hundreds of miles away. Recovery efforts continue with at least 15 people killed and dozens still missing. Determining the cause could take months.

But interviews with workers who had been on the site, together with early official findings, highlighted potential problems with construction design and quality.

At the center of the scrutiny is China Railway 10th Engineering Group, a Chinese state-owned company with about a dozen other projects in Thailand and whose contractors tried to remove documents from the site after the disaster.

Behind that Chinese company is its parent, China Railway Group — a Chinese infrastructure giant with soaring debt, a hunger for new projects and subsidiaries facing accusations of weak safety in several countries.

Workers in Bangkok told The New York Times that China Railway 10th, which was part of a consortium constructing the building, underpaid contractors who turned to lower quality materials, and used columns narrower than usual.

Thai officials testing twisted metal from the ruins said they found substandard steel bars — made by a Thai factory with Chinese owners that the authorities had shut down in December.