Police in the northern Chinese city of Tianjin have seized 600 computers used to mine Bitcoin, after abnormal electricity usage attracted the attention of the local power grid operator, CNBC reports April 25.

CNBC cites local media outlet Xinhua, which reported details from a local police officer saying that it was "largest power theft case in recent years,” and that “eight high-power fans” had also been seized.

Xinhua has not reported when the equipment was confiscated, but five people are reportedly under investigation and another has been detained.

Due to cheap electricity and hardware manufacture, China is a stalwart crypto mining superpower. A recent report showed that mining costs in China run to $3,172 per coin, which can offer miners a significant, if fluctuating, return.

In 2017, allegedly 50 to 70 percent of BTC mining took place in China. This January, however, news broke of the People’s Bank of China (PBOC)’s intent to toughen regional regulatory oversight and potentially restrict the power use of miners in future.