The amount of computing power dedicated to churning out new units of bitcoin has jumped close to an all-time high as cryptocurrency miners shift their operations to new countries following a clampdown in China.

The bitcoin hash-rate, a measure of how difficult it is to create new coins, has risen to 172m terahashes per second, the highest since May, according to data from Blockchain.com. The increase suggests digital “miners” are dedicating more computing resources to crack complex puzzles, for which they are rewarded with newly-minted bitcoin.

Miners have been moving to new geographies since May, when China outlawed the energy-intensive practice. The negative environmental impact of bitcoin mining has been a key sticking point for bitcoin critics, due to the amount of energy needed for producing new coins.