The company said several large tornados passed over the area Wednesday, however no fatalities were reported, although one worker at a surface operation received an injury that required first aid treatment.

No other injuries have been reported, officials said.

"While both the No. 4 and No. 7 [longwall] mines avoided direct impact by the tornadoes, they experienced power outages which have temporarily impacted production,” US operations president Walt Scheller said.

“We expect production to resume as soon as all power is restored and any related underground issues are resolved.”

The company also reported mostly superficial damage at its surface operations, except the Taft Choctaw mine where storm-related damage cut the power to the mine and the electrically-operated dragline.

“At this time we are uncertain how long it will take to restore power to this facility,” officials said, adding that its metallurgical coke plant in North Birmingham was unaffected and was operating at normal levels.

Florida-based Walter completed its $US3.2 billion acquisition of Canadian producer Western Coal earlier this month.

The newly combined company is a North American and global steelmaking coal giant, the top publicly traded pure-play metallurgical coal producer in the world with access to the Pacific and Atlantic seaborne markets.

In total, the producer now owns 385 million tons of reserves, 20Mt or more of which it expects to mine annually by 2012.

Its production profile is balanced between Walter's high-productivity assets and Western Coal's high-growth assets in Canada, the US and the UK, and it will be the only producer with cost-advantaged transportation access to the Asian and South American seaborne metallurgical coal markets.