At least one person was killed Tuesday at the KMCO factory in Crosby, Texas, Harris County sheriff Ed Gonzalez said.
Two others are in critical condition and were taken to a hospital by helicopter said.
The fire is included, she said, but the firefighters are working to spread.
Residents within 1 km of the factory were told to protect themselves, Harris County Sheriff's Office said. However, there does not seem to be any dangerous chemicals in the air.
"We have not seen any action-level discoveries," said Matt Loesel, coordinator of the US Environmental Protection Agency
. Moreno said it was dry and flammable chemicals in the warehouse where flames came.
"Our hearts and prayers go to those affected as well as to our first responders, employees and our community," said KMCO President John C. Foley. "We apologize for the inconvenience to local residents, and the well-being of our employees, neighbors and the environment remains our top priorities."
Pierre Meilhan of CNN contributed to this report.