Ten prisoners were taken to hospitals by ambulance, and nine were transported as "walking wounded" from Diboll Correctional Center to area hospitals, according to prison officials.
At 11:30 a.m., the sheetrock ceiling of one of the five housing units in the prison collapsed, according to Management & Training Corporation (MTC), which operates the prison.
"We are still trying to determine the cause of the collapse," said a statement by MTC.
A local fire official on the scene wasn't sure what may have caused the collapse, or whether it's related to heavy rainfall in Texas recently.
"It's not raining at all today here. We got a lot of rain yesterday. It's a new building, a new facility. I don't know why the roof would collapse," said Lufkin Fire Department Battalion Chief Jesse Moody.
David Driskell, the prison's warden, said, "It probably had a lot to do with the rain over the last couple days."
Diboll Correctional Center has a maximum capacity of 518 inmates and is managed by MTC, according to the Texas Department of Criminal Justice website.
MTC, a private contractor based in Centerville, Utah, manages 22 prisons in eight states, according to the company website, and also operates 21 Job Corps programs for the U.S. Department of Labor.