As of April 2, Thailand has recorded at least 21 deaths from last week’s earthquake. Just over half those deaths came from one location: an under-construction 30-story tower, developed by China Railway Engineering Group, through its Thai subsidiary China Railway No. 10 (Thailand), and local developer Italian-Thai Development (ITD).

The tower, located near Bangkok’s popular Chatuchak Market, dramatically collapsed following tremors from the earthquake, whose epicenter was over 1000 kilometers away. 

The skyscraper, meant to house the government’s State Audit Office, was the only building to collapse in the Thai capital city; other towers remained standing, even as videos of swaying buildings and rooftop pools spilling onto the streets below spread on social media.

Thai authorities now allege that contractors at the collapsed tower used substandard steel bars sourced from an already-shuttered factory. 

Samples of two different sizes of steel bars collected from the site failed quality tests conducted by the Iron and Steel Institute of Thailand, according to Bloomberg. 

Thitipas Choddaechachainun, the head of a working group at the Ministry of Industry, said the steel was supplied by a factory that had been closed since December, due to other safety violations. He did not identify the company.

ITD did not immediately respond to Fortune’s request for comment. China Railway Engineering Group could not be reached.

The death toll for Friday’s 7.7-magnitude earthquake now stands at over 2,700, the vast majority of which are in neighboring Myanmar. The epicenter was near Mandalay, the country’s second-largest city, and tremors were felt in China and Bangladesh, as well as Thailand. Myanmar has been mired in a civil war since 2021’s military coup. 

A Chinese connection

China Railway No. 10 (Thailand) began construction of the State Audit Office building, together with ITD, in 2020.

The Thai subsidiary’s parent company is linked to the Chinese state-owned China Railway Engineering Group (CREC), one of the world’s largest construction and engineering contractors. CREC is ranked No. 35 on Fortune’s Global 500.

According to Thai media reports, China Railway No. 10 (Thailand) has been awarded 13 government projects since 2018, and the 2.1 billion baht ($61.4 million) State Audit Office building was its highest-profile project in the country to date.

Companies linked to China have invested heavily in Thailand, especially against the backdrop of growing geopolitical uncertainty that started under the first Trump administration.

On Tuesday, Thai Prime Minister Paetongtarn Shinawatra instructed government agencies to investigate all construction projects awarded to China Railway No. 10, according to the Bangkok Post. The newspaper added that these projects include sections of Bangkok’s high-speed rail, and a building of the Office of the National Water Resources.

The local developer

ITD, the local developer involved in the construction of the State Audit Office building, is ranked No. 180 on Fortune’s Southeast Asia 500. The company, founded in 1958 by a Thai and Italian, helped to develop Bangkok’s Suvarnabhumi International Airport. ITD listed on the Thai stock exchange in 1994.

Yet the contractor has faced challenges in recent years. Some of ITD’s projects in Myanmar have been affected by the sudden imposition of military rule, leading to delays and shutdowns. The contractor faced cash flow issues last year that led to delayed payments for some workers and contractors.

ITD shares are down at least 25% since Friday’s earthquake and skyscraper collapse.