Altivia Chemical was working to contain a toxic gas leak from its LaPorte, Texas, plant on Dec. 4 as the city's emergency management agency ordered some nearby residents and five neighboring facilities to shelter in place out of caution.

Halliburton's Multi-Chem Bayport site, Stepan's Pasadena facility, and three others belonging to Kuraray Americas, Evonik, and NCTI, were sheltering in place after the offsite release of a toxic gas called phosgene, according to community alerts.

Located about 30 miles (48 km) east of Houston, La Porte's Office of Emergency Management (LPOEM) said the city issued a cautionary shelter-in-place until the amount of phosgene released is determined.

"A chemical emergency has occurred and residents south of Fairmont between Bay Area and S. 16th Street need to immediately shelter in place," LPOEM said on X, formerly Twitter.

Altivia could not immediately be reached for comment.

Phosgene is a colorless gas with a suffocating odor like musty hay that is used in the manufacture of other chemicals, pesticides, and pharmaceuticals, according to the U.S. Centers for Disease Control and Prevention.

Exposure to phosgene may cause vomiting, breathing difficulty, chest pain and, when liquid, frostbite.