Multiple people were injured when an escalator in a busy Hong Kong shopping center suddenly shifted into reverse, causing a human traffic jam. A total of 18 shoppers were injured when the packed escalator at Mong Kok's Langham Place switched directions Saturday, CNN reported. Amid an investigation into the cause of the escalator's malfunction, two mechanics have reportedly been arrested.

The mechanics, according to local police, may have "tampered with" the escalator following Saturday's incident. "The arrest of our mechanics was a surprise," Otis Elevator Company spokesperson Ian Fok told CNN in a statement. "While the mechanics were assisting the EMSD, the agency called the police to have the mechanics arrested. Our legal team is working with law enforcement to clarify the situation and intends to defend our mechanics." Both suspects are facing obstruction of justice charges and have since been released on bail. They are due to report back to police next month.

A man who suffered a head injury during the commotion was reported as being "in serious condition" by a CNN affiliate this weekend. "I heard people screaming," one witness told the South China Morning Post. "The escalator was going down but the speed accelerated." This sudden change in speed and direction, the witness added, caused shoppers to "panic." According to updated reports, two people are still in the hospital and listed as "in a stable condition."

Though an official explanation on the escalator pileup hasn't been released, BBC News reported city officials believe a damaged driving chain and a faulty braking device may have been the cause. The escalator had passed a safety inspection just days earlier. An investigation is ongoing.