An explosion at a chemical factory killed at least one person, injured 73 others and sent orange flames and plumes of black smoke billowing into the air in the US state of Louisiana on Thursday.
"As of now we believe every worker has been accounted for," Governor Bobby Jindal told reporters.
"Ten workers are still in a safe room in the plant. This is part of the emergency protocol to shut down the plant," he said.
The explosion occurred at the sprawling Williams Olefin petrochemical plant in at 8:37 am (1237 GMT).
Around 600 workers were on site when the blast rocked the sprawling facility in Geismar, an industrial area on the Mississippi River north of New Orleans.
Residents in the area told local media that they could feel their homes shake from the blast, and some saw a huge fireball engulf parts of the sprawling plant.
People living within a two-mile (3.2 kilometer) radius were told to stay inside, close their windows and shut down air conditioning units to protect themselves from potentially toxic smoke, but the order was lifted in most places a few hours later.
"We've completed our first round of monitoring," Jean Kelly, a spokeswoman for Louisiana's department of environmental quality, told AFP.
"We didn't see any spikes of chemicals in the air."
The shelter-in-place order was lifted for everyone except four other plants near the blast.
Thick black smoke continued to pour out of the petrochemical plant's smoke stack after the fire was extinguished, as workers burned off chemicals to make sure they didn't build up to dangerous levels.
Since the chemicals are mostly hydrocarbons they should not pose a significant inhalation hazard, Jindal said.
"Our thoughts and prayers are with the workers and their families," he said.
"There will be further investigations to determine what happened and make sure this doesn't happen again."
Jindal said it is too early to speculate what caused the explosion at the factory, adding "they don't even have a theory yet."
Workers were able to close the emergency shutdown valves and isolate the unit after the blast, the plant operator said.
"Our emergency response crews are thoroughly trained to respond to these types of incidents, and are diligently performing their work, with their first priority being the safety and well-being of people in and around the area," Williams Olefin said in a statement.
The facility produces approximately 1.3 billion pounds of ethylene and 90 million pounds of polymer grade propylene a year, according to the company's website.
The explosion happened two months after a blast at a Texas fertilizer plant killed 15 people -- including a dozen firefighters -- and injured 200 others.
The environment department had earlier reported that two people were killed in the blast -- one who was confirmed dead and a second who was missing and presumed dead.