DALLAS — A series of explosions at a gas facility sent flaming debris raining onto highways and buildings near downtown Wednesday and injured at least three people.

Authorities evacuated a half-mile area surrounding the Southwest Industrial Gases Inc. facility and shut down parts of nearby Interstates 30 and 35, snarling traffic for miles around one of the area’s busiest freeway interchanges.

Two unidentified patients were brought to Parkland Hospital in serious condition, said Robert Behrens, a hospital spokesman. A third man was taken to Methodist Dallas Medical Center, hospital spokeswoman Sandra Minatra said. She could not give out his condition.

Fire Department Lt. Joel Lavender said the accident was caused by a malfunctioning connector used to join acetylene tanks during the filling process. He said the three who were injured included the manager and a worker at the facility, as well as a truck driver.

The explosions began about 9:30 a.m. and continued for at least a half hour, sending burning gas cylinders and other debris flying like missiles onto highways, parking lots and nearby businesses.

“I thought it was artillery. It was just coming just boom, boom, boom,” said witness Tony Love, a former Army soldier.

By early afternoon, fire crews were hosing down the charred metal wreckage to extinguish lingering flames.

According to the industry Web site gasworld.com, Southwest Industrial distributes a range of gas products, including acetylene, helium and hydrogen as well as welding equipment. Calls to a phone listing for the company weren’t answered.

Despite hazy skies, a black column of smoke was visible from at least 10 miles during the blasts.

Jan Malone, a spokeswoman for the Texas Commission on Environmental Quality, said the gases posed no danger to the public. She said Southwest Industrial has been in operation since 1990 and had no violations with the agency.

The Environmental Protection Agency’s emergency responders were on the scene, and the U.S. Chemical Safety Board was sending a team of investigators as well.

Vanessa O’Brien said she was standing in a parking lot a few blocks away when she felt at least 20 vibrations from the explosion.

“We felt the whole building move and the windows rattle,” she said.

The Society for the Prevention of Cruelty to Animals closed a nearby office. Staffers and animals were moved to another side of the building and animals recovering from surgery were taken to another facility, the group said in statement.

Dallas County’s main jail and criminal courts building were at the edge of the evacuation zone but continued to operate, said Deputy Michael Ortiz of the Dallas County Sheriff’s Department.

Carol Peters, a spokeswoman for Oncor Electric Delivery, said about 30 buildings near the blasts were without power until fire crews fully extinguished the blaze.