SÃO PAULO, Brazil — A São Paulo subway train crashed into the back of another while approaching a busy station this morning, injuring at least 33, with two in critical condition with head injuries.
São Paulo's fire department said one of the trains had stopped between Carrão and Penha, two busy commuter stations on a subway line that serves over 1 million people each day, according to the Associated Press. The Metrô company said in a statement that it is investigating the crash but has yet to determine its cause.
More from GlobalPost: Train collision in São Paulo injures 38, puts two in critical condition
But according to Metrô syndicate director Alex Fernandes, the crash was caused by a mechanical failure that was perceived hours before the accident, reported Brazilian news site UOL. An operator at Carrão station noticed a problem with the subway's communication system called ATC, and that the problem was related to the Operational Center of Control of the Metrô.
In an interview with Brazil's TV Globo, Metrô president Peter Walker said the two trains should have maintained a minimum distance from one another, but that one stopped while the other behind it continued along the tracks.
"[The driver] said he received a "line free, continue" signal, so he continued," Walker told Globo.
According to the International Business Times, witnesses said the train that hit the other from behind was moving at a low speed. An unidentified passenger said people were "flying" when the trains crashed. Another passenger said many people panicked.