Up to 17,000 people were told to evacuate homes in the town of Apex in the US state of North Carolina after a blast at a chemical plant.
At least 18 people were injured in Thursday's explosion which sent chemical clouds high into the sky.
Officials said the cause of the blast was not clear and the fire that resulted might take days to extinguish.
Evacuation orders were issued overnight. Those staying at home were urged to close all windows.
Residents were also urged to turn off air conditioning units and look out for symptoms of chemical poisoning.