It happened around 12:30pm at Watco Mechanical Services in the 17000 block of Premium Drive in Hockley.
Three Life Flight helicopters were called to the scene, officials said.
According to the company's website, the plant repairs railcars. Emergency responders at the scene said the three victims were in a paint booth under construction when paint dust caught fire.
The extent of their injuries was unknown.
No other details were released.
Please stay with Eyewitness News and abc13.com for updates.