At least 20 people have been killed and more than 30 injured after a Bolivian Air Force Hercules C-130 transport plane crashed while attempting to land near the capital, La Paz.

The aircraft was trying to land Friday evening at El Alto International Airport when it skidded off the runway during severe weather and ploughed into a busy highway, authorities said. Heavy hail and lightning were reported at the time of the crash.

Police Colonel René Tambo said the death toll stood at “about 20, maybe a few more,” while dozens were taken to hospital with injuries. The plane eventually came to rest in a nearby field after veering off the runway, according to Defence Minister Marcelo Salinas.

The Hercules was transporting a cargo of newly printed banknotes. In chaotic scenes captured on social media, onlookers gathered at the crash site, with some reportedly collecting scattered bills from the wreckage. Authorities used water hoses and tear gas to disperse crowds and prevent looting. Click here for video.

The Ministry of Defence later clarified that the transported money had no official serial numbers and therefore “has no legal or purchasing power,” warning that possessing or using it would constitute a crime.

Two of the six crew members remain unaccounted for. The cause of the crash is under investigation. La Paz, located at 3,650 metres above sea level, is the world’s highest administrative capital.