By Yongchang Chin

Shares of Chinese coal companies were weaker Wednesday after Beijing said it would intervene to boost coal supply and cool prices in the wake of shortages that have forced blackouts in parts of the country and weighed on economic growth.

Hong Kong-listed shares of Yanzhou Coal Mining dropped 10%, China Coal Energy lost 9.9% and China Shenhua Energy fell 4.8% on concerns that lower coal prices could weigh on revenues. The companies' Shanghai-listed shares fell by by 10%, 9.9% and 6.7%, respectively, by the mid-day break.

China's National Development and Reform Commission said on its website late Tuesday that it would help energy producers raise output and shore up domestic supply, as well as "guide coal prices back to a reasonable level" and clamp down on speculative activity.

It said it would focus on investigating "abnormal transactions," referring to market actors potentially hoarding resources to drive prices up.

The prospect of Beijing's intervention is already weighing on coal prices, ANZ said, noting that Newcastle coal futures were 4.0% lower at $229.90 a ton, although it is still up 30% from a month ago.

China's power supply crunch is likely to persist into the winter, Citi Research said, as shortages could force the government to mandate a 12% cut in industrial power use this quarter, with deeper cuts possible depending on the weather.

"This would increase stagflation risks and growth pressures on the Chinese and global economy over the coming winter," Citi said.

Write to Yongchang Chin at yongchang.chin@wsj.com

Corrections & Amplifications

This item was corrected at 0509 GMT to reflect Hong Kong-listed shares of Yanzhou Coal Mining dropped 10%. The original version incorrectly referred to the company as Yanzhou Coal Ming in the second paragraph.

(END) Dow Jones Newswires

10-20-21 0046ET