It all started with a whistleblower’s revelation on social media that the subway system in Xi’an, northwestern China’s most populous city, was built with poor-quality parts that put commuters at risk.

The post has landed eight people in police custody, and on Tuesday, a visibly emotional company representative apologized on local TV, even kneeling before the camera. Electrical wiring worth some 30 million yuan (about $4.3 million) in the city’s subway system did not meet official standards, he said.

The organizations in charge of the subway systems of Xi’an and one other city have since announced they will replace their faulty wiring.

On March 13, an anonymous net user claiming to be an employee of Shaanxi Aokai Cable Co. Ltd. posted on online forum Tianya that the Xi’an subway wiring on Line 3, which opened last year, was substandard. The original post was later deleted, and the identity of the whistleblower could not be confirmed, but the message was nevertheless spread online.

Titled “Do you still dare to take the Xi’an subway?” the post explained that the thinness of wiring was a fire hazard, and implied that the owner of the company that supplied the wiring had gotten away with the defects due to his connections to Xi’an Metro, the state-owned company that runs the city’s subway system.

Aokai initially said its cables had passed tests from the local Administration of Quality and Technology Supervision, and that company representatives had contacted the authorities to report “an attack on our business reputation.”

But in a press conference on Friday, Xi’an deputy major Lü Jian announced that an investigation had been launched and wiring samples had been sent for testing. When the results were made public on Monday night, five samples from the low-voltage electrical wires of Line 3 were found to be substandard.

Yang Xin, the secretary of the city’s commission for discipline inspection, said that after the test results were released, the police shut down the company’s operations and took eight people into custody. Yang said that the investigation would examine all past projects that Aokai took part in and look into potential abuses of power by state officials.

According to Aokai’s website, the company has worked with subway and railway companies in several other cities, such as Chengdu and Chongqing in southwestern China, and has provided services for a number of state-owned enterprises. Aokai was founded in 2012; its first contract was for Line 3 of the Xi’an subway.

The general manager of Xi’an Metro, Song Yang, said that the company will replace the cables overnight, but that the defective wiring posed no safety threat.

On Wednesday, three contractors involved in building Chengdu’s subway system, which used cables from Aokai, announced that they would immediately replace the cables and had canceled plans to work with Aokai on a new tram line.

Since China’s first subway line was built in Beijing four decades ago, more than two dozen Chinese cities currently operate subway systems, and a dozen other cities have begun planning or construction of their first subway lines.

Online reactions to the Xi’an wiring scandal were mixed, with some net users calling for severe punishment of those involved, and others questioning the whistleblower’s identity.

Some netizens praised Xi’an’s new Party secretary, Wang Yongkang, for the city’s unusually swift reaction. “This is the efficiency revolution that started with picking up cigarette butts,” a Xi’an net user wrote on microblog platform Weibo, referring to previous news of Wang personally collecting discarded cigarettes to clean up the city. Wang has been in office since December.

In February, three high-level environmental protection officials in Xi’an were removed from their positions after their lax oversight of area wastewater was exposed on a TV show.

Editor: Kevin Schoenmakers.

(Header image: An aerial view of a metro station under construction on Line 3 in Xi’an, Shaanxi province, Dec. 18, 2015. VCG)