An explosion rocked an oil refinery Monday in a violent blast that shook buildings miles away, authorities and witnesses said. There were no immediate reports of injuries.

"All I know is that it blew up," a Howard County dispatcher said.

The 8:30 a.m. blast sent black smoke billowing into the sky, shut down a major interstate and left residents rattled.

"It was extremely scary. You shook you were so scared," said Laura McEwen, the wife of Mayor Russ McEwen who lives about two miles from the refinery. "Our walls shook. It jolted your bed. It was like an earthquake."

John Moseley, managing editor of the Big Spring Herald whose downtown office is also about two miles from the refinery, said, "I thought it would knock the walls down."

The refinery, owned by Dallas-based Alon USA, employs about 170 people and produces about 70,000 barrels a day. Company spokesman Blake Lewis said he didn't know how many people might be at the plant at the time.

Lewis said the company had an unconfirmed report of an incident but did not know any details. A plant manager was on the way to the site, he said.

Interstate 20 was shut down near the plant, Big Spring police spokesman Roger Sweatt said. His department didn't know of injuries.

"There's some fire and a whole bunch of smoke," Sweatt said.

Big Spring is about halfway between Dallas and El Paso.