An accident at a northern China mine has left at least 20 people dead and 30 injured Saturday, according to The Associated Press. A bus transporting some 50 miners underground lost control and crashed into the wall of a tunnel due to malfunctioning brakes, the AP said, citing China’s state media agency. China’s Ministry of Emergency Management has deployed a team to “guide and assist” in rescue and investigative efforts, state media reportedly said. Yinman Mining Company operated the site, which produced silver, lead and zinc. Company execs are now under travel restrictions during the investigation, per the AP.