(CNN) A blast at a construction site on a central Texas hospital campus killed one person Tuesday, officials said.

Twelve construction workers were injured, at least three to four critically, according to Dr. Jeffrey Bates, chief medical officer at the Coryell Memorial Healthcare System in Gatesville, west of Waco.

No patients or staff were injured, he said.

The blast occurred shortly after 2 p.m. in a construction area behind Coryell Memorial Hospital, according to hospital officials. Dark smoke billowed from the area.

"This was clearly in the construction area. Construction workers were the ones that were injured," Bates said.

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