LOS ANGELES (Reuters) - A utility worker was killed and 15 other people were injured on Monday when a ruptured gas line triggered an explosion that leveled a house and shattered windows in nearby homes in the Southern California town of Murrieta, authorities said.

The blast sent flames shooting some 30 feet (9 meters) into the air, and, according to media reports, rocked the surrounding Riverside County neighborhood with such force that some residents initially mistook it for an earthquake.

The gas rupture was believed to have been caused by a contractor digging at the home without first calling to have underground utility lines marked, as required by law, according to the Southern California Gas company.

City firefighters responding to reports of a gas line breach were already at the house when SoCalGas employees arrived to make repairs. The explosion occurred about 30 minutes later, Murrieta Fire and Rescue Deputy Chief David Lantzer told a news conference.

Murrieta is about 80 miles (130 km) southwest of Los Angeles.

One of the gas company workers on the scene was killed and 15 other people who were hurt in the blast - three of them firefighters - were taken to hospitals for evaluation, fire and utility officials said. Their conditions and the severity of the injuries was not disclosed.

Contrary to early news reports that an occupant of the house may have gone missing, SoCalGas spokeswoman Christine Detz said authorities later determined everyone was accounted for.

Television news footage from the scene showed firefighters dousing the charred, mangled ruins of the house with water as one wall remained standing. A house next door also appeared to have been damaged.

Lastacia Neat, 47, who lives across the street and two houses down from the one that blew up, told the Riverside Press-Enterprise newspaper the explosion shattered windows throughout the neighborhood.

Another neighbor, Kevin McKinney, 63, who lives next door, said in an interview with Los Angeles television station KABC-TV that he was startled by the sound of “one big, loud boom, and then glass flying.”

“It rocked the house, good,” he said.