A natural gas line in north Texas erupted Monday, killing at least three people and lighting up the sky with orange flames, officials said.

An unknown number people were missing, and officials feared the death toll could rise.

Workers apparently hit the underground line about 50 miles (80 kilometers) south of Dallas while digging on Monday, said Cleburne City Manager Chester Nolen. The heat was "unbearable," even 300 yards (meters) from the flames, he said. A column of gray smoke was visible miles (kilometers) away.

About six people were taken to hospitals, Johnson County Emergency Management Coordinator Jack Snow, said. At least three people died "and there could be more," Nolen said. An unknown number of people remain unaccounted for, Nolen said.

Laura Harlin, a resident of nearby Granbury, said she heard a "huge rumbling" that initially sounded like thunder and then like a tornado because it lasted so long.

"For about 10 minutes, it was so loud that it was like there was an 18-wheeler rumbling in your driveway," she said.

Also Monday, seven workers were burned when a crew drilling a natural gas well through an abandoned coal mine in West Virginia hit a pocket of methane gas that ignited, triggering an explosion. The explosion happened about 1:30 a.m. in a rural area about 55 miles (88 kilometers) southwest of Pittsburgh. A column of fire shot at least 70 feet (21 meters) high, but the flames fell to 40 feet (12 meters) within hours. Gas continued to burn late Monday afternoon.

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Associated Press Writers Jeff Carlton and Schuyler Dixon in Dallas contributed to this report.