BEIJING (AP) — Chinese authorities have commandeered supplies of natural gas to heat homes, disrupting supplies to industry, after efforts to clear smog-choked air by banning coal use led to energy shortages in frigid weather.

Utility companies in areas throughout China have reduced or cut off gas supplies to factories and other industrial customers.

The disruption highlights the difficulties of massive government efforts to clean up China's smog-choked cities and reduce reliance on coal.

The latest shortages stem from a four-year campaign launched by Beijing in 2013 to shift some 3 million households in China's north to gas, which has boosted demand while supplies failed to keep pace.