HOUSTON (AFP) - The operators of a flooded chemical plant outside Houston warned on Wednesday they were dealing with a "critical issue" triggered by Harvey's torrential rains and have no means to prevent a possible explosion at the site.

As a precautionary measure, officials had already ordered the evacuation of an area within three km of the organic peroxides plant in Harris County, which is owned by French group Arkema.

Mr Rich Rowe, president and chief executive of Arkema Inc, said in a statement that the facility in the town of Crosby, north-east of Houston, had been evacuated for employees' own safety following a dangerous loss of on-site refrigeration.

The company manufactures compounds with a broad array of commercial uses, including plastics, pharmaceuticals and construction materials, which can combust if not cooled to the proper temperatures.

Multiple fail-safe measures had broken down as a result of the flooding, according to Mr Rowe.

"Right now, we have an unprecedented six feet of water at the plant," Mr Rowe said. "We have lost primary power and two sources of emergency backup power."

"As a result, we have lost critical refrigeration of the materials on site that could now explode and cause a subsequent intense fire," he added.

"The high water and lack of power leave us with no way to prevent it."

Mr Rowe offered apologies to "everyone impacted" and that the company was working with authorities to manage the situation.