An explosion at a chemical plant Tuesday injured 14 workers and set off a fire that spewed thick black smoke, leading to the temporary evacuation of nearby residents, officials said.

Two of the workers were seriously injured, plant vice president Randy Cox said.

Windows were blown out as much as a third of a mile away, and a house across the street from the plant was moved off its foundation.

The fire was mostly extinguished by mid-afternoon and all workers at the Synthron Inc. plant were accounted for. The cause of the blast hadn't been determined, police Capt. Ronnie Rector said.

Officials allowed residents who had voluntarily evacuated to return to their homes. They were advised to keep their windows closed and ventilation systems turned off, said police Sgt. Scott Rogers.

State water and air quality officials were at the site, monitoring conditions and checking to see whether runoff into creeks posed any threat to the nearby Catawba River, the source of drinking water for much of central North Carolina and South Carolina.

The U.S. Chemical Safety and Hazard Investigation Board said it was dispatching a team from Washington to assess the explosion and fire.

Cox, who said he was thrown from his chair by the blast, told reporters that the plant's maintenance chief had been burned and the plant's manager suffered head injuries. They were hospitalized. The 12 with less serious injuries, including Cox, were treated and released.

Synthron is a subsidiary of Paris-based Protex International, which produces specialty chemicals in the United States, Europe, Asia and North Africa. There was no immediate response to calls seeking comment from Protex headquarters in Paris after business hours.

Rector said the plant produces predominantly textile chemicals. He said the chemicals it has on hand include toluene, a petroleum-based liquid that can be explosive.

The plant's last state Labor Department violation was in 1996; the company also was fined in 2001 and 2002 for violations in handling hazardous waste and has been fined four times since 2001 for violating air emission limits.