Chemicals have been released into the atmosphere from a flood-damaged plant near the storm-hit US city of Houston, local officials say.
Earlier, black smoke was seen issuing from the Arkema chemical plant at Crosby.
A police officer who was helping secure the site was taken to hospital after inhaling fumes, while nine others admitted themselves as a precaution.
Arkema said this was believed to have been caused by a “non-toxic irritant”.
Harris County sheriff Ed Gonzales said the release was not believed to have been a result of an explosion, despite earlier reports of blasts.
Residents living within a 1.5-mile (2.4km) radius of the plant were evacuated after the company warned there was a risk of explosions and fire.
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During heavy rainfall from Hurricane Harvey, the complex lost the ability to refrigerate chemical compounds that need to be kept cool.
In an earlier statement, Arkema said: “At approximately 2am CDT [07:00 GMT], we were notified by the Harris County Emergency Operations Center of two explosions and black smoke coming from the Arkema Inc plant in Crosby, Texas.
“We want local residents to be aware that product is stored in multiple locations on the site, and a threat of additional explosion remains.
“Please do not return to the area within the evacuation zone until local emergency response authorities announce it is safe to do so.”
Door-to-door search
At least 33 people have been killed in eastern Texas in the aftermath of the storm, which the US National Weather Service has now downgraded to a tropical depression.
Heavy rainfall is expected from Louisiana to Kentucky over the next three days, and flood warnings remain in effect for south-east Texas and parts of south-west Louisiana.
US energy supplies have been hit, as oil companies shut down refineries and a major pipeline in the Houston area.
Firefighters are due to begin a door-to-door search of badly flooded areas of Houston on Thursday, to rescue survivors who are still stranded and recover the bodies of those who have died.
“We’ll be doing block-by-block, door-by-door search of streets… to make sure there are no people we’ve left behind,” Richard Mann, the city’s assistant fire chief, was quoted as saying by the Houston Chronicle newspaper.
“This will be a one- to two-week-long process to make sure we address all those areas that have been… most impacted.”
What happened at the chemical plant?
The Arkema chemical plant, 21 miles from Houston, shut down production on Friday before the storm made landfall.
But 40in (102cm) of rainfall in the area had flooded the site and cut off its power, the company said. Back-up generators were also flooded.
