Police in eastern China busted a bitcoin mining operation following a surge in local electricity usage, according to a wire report from Agence France-Press.

The police, who confiscated 4,000 “mining devices,” allege the mining farm misappropriated nearly 20 million yuan ($3 million) in electricity costs. The investigators learned of the theft from a local power provider.

“In value, it is the largest case in the amount of electricity stolen that Jiangsu has cracked since the founding of New China, and a rare sight in the whole country,” Zhenjiang police reportedly said to AFP.

Investigators allege more than 20 people participated in this particular mining operation.

Bitcoin mining is still popular in China. Coinshare, an investment platform, published a report that found 50 percent of the global bitcoin computing power was located in southern China.

Recently, with bitcoin’s surge in price to around $12,000 the difficulty of the algorithm reached record highs, as the bitcoin software automatically adjusts its mining difficulty, approximately every 14 days, based on the amount of computing power in the network.

As previously reported, the total hash rate this year could peak to a threshold of 70EH/s in August, meaning another 300,000 mining machines could be activated to meet the needed hashing power.