At least one person is dead and two critically injured after a chemical plant fire on the outskirts of Houston, officials said.

The blaze at the KMCO plant was caused by a fire in a tank of colorless flammable gas isobutylene and broke out around 11 a.m. Tuesday, according to the Harris County Sheriff's Office.

The Harris County Fire Marshals Office lifted a shelter in place order for those within a mile radius of the plant a little after 3 p.m. local time. The order included closing any windows or doors as well as turning off air-conditioning units.

Harris County's emergency management office announced at about 4 p.m. that the fire had been contained and first responders were working to prevent the flames from spreading to nearby chemical tanks.

Authorities said at least one person was killed Tuesday when isobutylene ignited and exploded at a chemical plant in Crosby, Texas. KPRC

The agency previously announced a 1-mile "no-fly" zone above the plant. Students at all nearby Sheldon Independent School District campuses were initially not permitted to leave school buildings, according to the district.

Later, during a midafternoon press conference, Sheriff Ed Gonzalez said authorities were working with the school districts "to make sure that we can get those children into their parents’ arms and get them back home as quickly as possible."

Gonzalez wrote on Twitter that a transfer line ignited in the area of the tank of isobutylene "and the tank caught on fire. An adjacent storage building with solid goods also caught fire."

Among the victims, one died at the scene of the fire and the two injured were airlifted for treatment, the sheriff said.

The KMCO plant has had several compliance violations with the EPA in recent years. An EPA report from last year listed some violations over the last several years of the Resource Conservation and Recovery Act, which dictates the management of hazardous materials and non-hazardous solid waste.

Previous inspections showed KMCO also had violations in regard to the Clean Water and Clean Air acts.

Harris County sued KMCO in 2008 for discharging wastewater that exceeded limits on certain pollutants, including ammonia, copper and zinc. KMCO settled with the county in 2009 and agreed to pay $50,000 in civil penalties for violating the state's environmental regulations, according to court documents.

KMCO also agreed to pay attorney fees and give $75,000 to a supplemental environmental project.

The county filed another lawsuit against KMCO in 2017, claiming the plant once again violated the state's clean water and air regulations. That case is still pending and is scheduled for a trial in June of this year.