Hundreds of firefighters and emergency medical workers rushed to the 28-year-old West Pharmaceutical Services factory, where officials estimated 134 people were on duty when the explosion occurred.
"It was terrible. I was just praying to get out," a 45-year-old factory worker told reporters. "Everything went black. It happened so quickly."
"We're talking about complete and total body burns," said an emergency room physician. "It's as if they were trapped inside an exploding canister."
The Kinston plant had been cited for 22 serious safety violations by a state inspector in November, but state officials say the problems were corrected more than a month ago. Most of the citations were for lack of procedures, signs and equipment required to keep workers safe around machinery in the plant, which made syringe plungers and IV supplies.
The violations would not likely have increased the risk of an explosion, a spokesman for the state Labor Department told reporters.
Helicopters airlifted dozens of victims who sustained critical injuries and serious burns. Following the explosion, a raging fire punctuated by bursting fireballs consumed the plant, as well as nearby trees and brush.
Ten people remained in critical condition early Thursday.
Some of the injured had second- and third-degree burns over up to 60 percent of their bodies, and one person had his arm blown off, doctors said.
"It was like a scene you never want to see in your life," said Lenoir Memorial Hospital emergency room physician Vicky Lanier. "It's amazing that more of those people weren't killed. Somebody somewhere was looking out for them."
Shock waves from the blast were so intense that they reportedly blew in doors of homes more than a mile away and shook classroom windows at the local high school.
"It smells like a bunch of rubber," one witness told reporters. A teacher in a nearby school described the explosion as "a clap of thunder magnified probably ten times."
The U.S. Chemical Safety Board immediately dispatched a team of chemical accident investigators to the scene, including CSB Chief Operating Officer Charles Jeffress, the former head of both North Carolina and federal OSHA.
The cause of the blast is still under investigation. The FBI, North Carolina State Bureau of Investigation, OSHA and other agencies also sent investigators.
West Chief Executive Officer Don Morel said the cause of the explosion is a mystery because the plant keeps relatively little volatile material on site, according to the Associated Press.
The plant is located in an industrial park on the outskirts of Kinston, a town of about 25,000 people 75 miles southeast of Raleigh.