An Enbridge-owned gas pipeline ruptured early Thursday in Kentucky, causing a massive explosion that killed one person, hospitalized five others, destroyed railroad tracks and forced the evacuation of a nearby mobile-home park, authorities said.

The blast was near Moreland, about 70 miles south of Louisville.

"The part of the area that has been compromised, there's just nothing left," said Lincoln County Emergency Management Director Don Gilliam. "The residences that are still standing or damaged will be accessible. There doesn't really look like there's any in-between back there."

Enbridge spokesman Jim McGuffey said two other nearby gas lines don't appear to be affected but will be inspected. He said there is no indication of what might have caused the explosion.

The blast also damaged railroad tracks, forcing 31 trains to back up overnight, authorities said. Crews were working to repairs the tracks. Kentucky State Police spokesman Robert Purdy said the track should reopen later in the day.

At least five homes were completely destroyed and several agencies are investigating to determine what caused the explosion, Purdy said. The National Transportation Safety Board said it is sending three investigators to the site.

The Kentucky explosion is the fourth rupture on an Enbridge natural gas pipeline in less than a year.

In January, a pipeline in rural eastern Ohio exploded, injuring two people and damaging two homes. Both the Ohio and Kentucky explosions were on the Texas Eastern Pipeline system, which runs from the U.S. Gulf Coast to the Northeast and mid-Atlantic, and came under Enbridge's wing when it bought Spectra Energy Partners late last year.

In December, another former Spectra pipeline ruptured and forced evacuations in rural northern Tennessee; no one was injured. And in October, an Enbridge pipeline in a remote part of British Columbia exploded.

Calgary, Alberta-based Enbridge is North America's largest pipeline operator and its main Canadian-U. S. oil pipeline corridor crosses northern Minnesota. Enbridge plans to build a new $2.6 billion pipeline to replace its existing Line 3 across the state, though the controversial project is currently in a sort of regulatory limbo.

It took hours for firefighters to douse the flames from the explosion, with trucks repeatedly refilling their tanks and returning to the scene.

Includes reporting from Star Tribune staff writer Mike Hughlett and the Associated Press.