Two explosions were reported early Thursday morning at a French-owned chemical plant at the city of Crosby, about 20 miles northeast of downtown Houston.
Black smoke is visible around the plant, the Harris County Sheriff's Office said.
There is a possibility of more explosions.
One deputy was taken to a hospital after being overcome by noxious fumes; nine other deputies are getting immediate medical checkups after complaining about "headaches and dizziness, according to a Miami TV station which had reporterJulia Bagg near the plant when the explosions were heard.
Residents in homes within a one-and-a-half mile radius around the plant were evacuated Wednesday after it became clear that the plant would explode, catch fire or both.
Workers were also evacuated from the Arkema SA site, owned by a French specialty chemicals company, which works with substances described as organic peroxides at the plant, chemicals sensitive to heat and water and can become explosive when exposed to both.
After flooding and loss of power Sunday, the chemicals then posed the possibility of a dangerous chemical reaction because refrigeration requirements had been violated by lack of electricity, the failure of a backup generator and then the failure of a mobile refrigeration vehicle.
Roads around the chemical plant are flooded, making access dangerous.
Arkema says there was nothing it could do to stop the chemical reaction that led to the explosions.
There are a number of homes within a mile of the plant.
The plant has been closed since Friday when operators shut it down in anticipation of Hurricane Harvey.
In a statement Tuesday afternoon, the company said:
"The situation at the Crosby site has become serious. In order to ensure the safety of our ride-out team, all personnel have been evacuated from the site at this time.
"Refrigeration on some of our back-up product storage containers has been compromised due to extremely high water, which is unprecedented in the Crosby area.
By Mike Shiloh
Copyright August 31, 2017, Mike Shiloh, Texas Energy Report LLC, www.texasenergyreport.com, All rights are reserved