Four people in northwestern China have been detained on suspicion of stealing electricity to mine bitcoins, local media reported. Investigations began on Wednesday after police in Yan’an, in Shaanxi province received a tip-off about unusual consumption of electricity in one of the oilfields owned by PetroChina Changqing Oilfield Company, chinanews.com reported. During a police patrol, police found a “bitcoin mine” at a hilltop, in which a power transformer was connected to a number of machines, Zhao Xiaobo, director of Yanhe Police Bureau in Yan’an, told the news website. The discovery has led to a wider investigation involving a special task force and online police, who later found several “bitcoin mines” hiding in several oilfields where machines running the software used to generate the crypto-currency were illegally connected to the oilfield’s power system, the report said. Some 1,600 bitcoin mining machines, as well as seven power transformers and network switches have been confiscated and four people have been placed under criminal detention, police said, without giving details of their identities. China calls for reining in risks in surging bitcoin market The incident, which police said they are still investigating, sheds the light over the booming bitcoin mining industry in China, now one of the largest such markets in the world. The digital currency was designed to be independent of the world’s banking systems and is generated by machines that solve mathematical problems, adding a record to a blockchain, and are rewarded with a certain number of bitcoins in return. The relatively low electricity price would also be one of the reasons behind the expanding cryptocurrency mining market in China, as bitcoin mining facilities often require enormous amounts of electricity. This could also explain why many bitcoin mines are often found established in the areas with abundant power supplies, such traditional mining areas or regions close to hydroelectric plants, according to mainland media. Bitcoin cash and the ‘civil war’ that is disrupting digital currency Areas such as Sichuan, Tibet and Inner Mongolia have reportedly hosted some of China’s largest-scale bitcoin operations. In February, National Business Daily reported that tens of thousands of bitcoin mining machines were working day and night in the mountainous area next to a hydroelectric power plant in Mabian Yi Autonomous County in southwestern China’s Sichuan.