At least two workers at a Houston-area oil refinery were killed when hydrogen sulfide leaked at the plant, setting off urgent warnings for nearby residents to stay indoors before authorities determined the public wasn't in danger.

A leak of toxic hydrogen sulfide on Thursday at the Pemex refinery in Deer Park, Texas, caused the deaths of two workers and injured 13.

Pemex's Deer Park oil refinery near Houston discharged 43,500 pounds of highly toxic hydrogen sulfide gas over more than seven hours in a deadly incident earlier this week, according to the Mexican state-owned company's disclosure to a Texas regulator.