A long-distance passenger bus crashed into the wall of an expressway tunnel in China's northwest, killing at least 36 people and injuring 13 others, official media reported Friday. The front end of the red bus was left mangled after it ploughed into the wall at the entrance to the tunnel on a four-lane highway, according to photos published by state media. The crash occurred in Shaanxi province shortly before midnight Thursday as the bus with a legal carrying capacity of 51 people was on its way to Luoyang, a city in central China, from Chengdu, the capital of the southwestern province of Sichuan. Such long-distance buses are a common mode of transport, particularly for migrant workers and other Chinese with low incomes. The Xinhua News Agency and other media outlets said the bus was the only vehicle damaged, although it wasn't clear if any other vehicles were involved in causing the crash. Photos on news websites showed it being towed out of the tunnel with no sign of it having caught fire. Two children were among those killed, and all the injured had been taken to a hospital, the reports said. Minister of Public Security Guo Shengkun ordered a swift investigation into the accident, according to state broadcaster China Central Television.