Shanxi Province, which is China's major coal-producing region, detected illegal mining activity with unmanned aircraft, the provincial land and resources administration said Thursday.

Two unmanned helicopters purchased last year were used in surveillance flights, with six specially-trained staff making 14 flights and exploring more than 2,000 square kilometers, the administration said. It did not say how many illegal mines were detected.

Aerial photos taken by the helicopters revealed illegal mines, which operated only at night. Many were dug into mountains, sheltered inside buildings or tunneled beneath courtyards, the administration said.

Shanxi accounts for one third of China's coal output, with frequent accidents in illegal mines despite government efforts to improve safety.

Source: Xinhua