Brewing strike action in the coal sector is "deeply concerning", Public Enterprises Minister Malusi Gigaba said on Friday.

"I am deeply concerned about the industrial action that has kicked off in the coal sector," he told reporters in Johannesburg.

Coal is a critical input in electricity production.

Speaking at power parastatal Eskom's report on the state of the electricity supply going into summer, Gigaba urged the mining sector to resolve the industrial action taking place at some coal mines in Mpumalanga.

Eskom CEO Brian Dames, said the utility had been closely watching coal mines as wildcat strikes in the mining industry hit South Africa over the past two months.

"We have seen some protest action on some coal mines over the last week or so," he said.

Coal deliveries to power stations had already been put at risk by the transport workers' strike, which ended on Friday.

Eskom had lost a day's supply of coal due to the transport strike.

If the coal strikes continued it would have a severe impact on the security of coal supply and commodity prices, Gigaba said.

"The sustainable price and supply of coal over the next five years is critical, and has been cited as pivotal for the management of electricity prices going forward," he said.

The minister urged the mining sector to resolve workers' concerns.

President Jacob Zuma said on Thursday that R118-million in coal production had been lost due to strikes from mid-September.