More than 5,000 residents were evacuated after a freight train carrying a "highly flammable and toxic gas" partly derailed and caught fire early Thursday just outside Knoxville, Tennessee, officials said.
Seven officers were taken to hospital after breathing in fumes from the blaze, Blount County Sheriff's Department spokeswoman Marian O'Briant told NBC News.
An evacuation zone is in place over a two-mile radius from the derailment, near Maryville, and could be in place for up to 48 hours, the fire department said.
Two shelters were being opened for residents including one at a local high school, according to David Kitchen, senior disaster program
The train was carrying Acrylonitrile — which authorities described as a "highly flammable and toxic gas."
The EPA says the substance is used in the manufacture of acrylic fibers and if inhaled in high levels can cause membrane irritation, headaches, nausea and kidney irritation.
Up to three cars were ablaze, O'Briant said, but it was no immediately clear if the fire was under control.
The CSX train was traveling from Cincinnati, Ohio, to Waycross, Georgia, and consisted of two locomotives, 45 loaded rail cars carrying mixed freight and 12 empty rail cars, company spokeswoman Kristin Seay told NBC News. One car derailed, she said.