No staff were believed inside the EQ Industrial Services plant in the town of Apex when the fire broke out late on Thursday, though officials say 25 people were taken to hospital with respiratory problems.

One evacuated resident, Matt Silliman, expressed his concern about the extent of the damage.

"At first we thought it was a gas line, and I figured, that's bad enough as it is, because of carbon monoxide poisoning. Then when I heard it was something like chlorine my first thought was this is not good, Apex is going to be destroyed."

Area schools and downtown Apex were closed Friday morning, with police cordoning off the area as flames continued burning at the plant.

The town's mayor, Keith Weatherly, says heavy rain which fell after the accident would help clear the air.

The company EQ Industrial Services Inc. handles industrial waste, from paints to solvents, as well as house chemicals, such as chlorine, pesticides and fertiliser.