Two people were killed and four remain in the hospital from an explosion at a manufacturing facility in Louisville, Kentucky, officials said.

       The "hazardous materials incident" was reported Tuesday afternoon at a Givaudan Sense Colour facility, a natural food coloring plant, according to the Louisville Metro Emergency Services.

       First responders were initially told by the business that all employees were accounted for, officials said Wednesday. But then a second victim was found buried in rubble late Tuesday evening after crews went back to the scene upon guidance from the business that someone was likely still there. It took three-and-a-half hours to remove that victim from the rubble, officials said.

       "We are deeply saddened to share the news that two of our team members lost their lives in this accident," Givaudan Sense Colour said in a statement.

       The University of Louisville Hospital said it received seven patients with injuries including burn and blast wounds. All those injured are employees of the plant, officials said.

       Four people remain hospitalized on Wednesday, all in stable condition, officials said.

       The cause of the explosion remains under investigation, officials said.

       Drone footage taken by Louisville ABC affiliate WHAS showed extensive damage to the facility.

       Residents within two blocks of the facility were evacuated, officials said. A shelter-in-place order was also issued for those within a 1-mile radius of the facility but it has since been lifted, officials said.

       Air monitoring is clear at this time, officials said.

       ABC News' Ahmad Hemingway and Jessica Gorman contributed to this report.