A second explosion rocked an underground gas storage facility early Friday, forcing authorities to expand evacuations around the blaze that continued burning a day after an initial blast triggered by leaking gas.

The fire at Duke Energy's (search) Moss Bluff storage facility intensified overnight, an official said. The second explosion was reported at 1:15 a.m and was seen as far as 20 miles away, witnesses said.

Everyone within a three-mile radius of the facility was being evacuated after the second blast and additional shelters were being set up, authorities said. The first explosion had prompted evacuations within a one-mile radius and surrounding highways were closed.

"We assume there are over 100 people" in the new evacuation order, a Liberty County Sheriff's Department dispatcher said.

The first blast at the facility early Thursday sent flames 150 to 200 feet into the air, awakening residents. An employee was making his rounds at the natural gas storage facility when the fireball erupted about 4 a.m. He escaped unharmed, said sheriff's Capt. Bill Tidwell. "Everybody's been accounted for," he said.

It could take days before the blaze burns itself out, firefighters said. Workers have shut off the supply of gas feeding the underground storage cavern, which holds 6 billion cubic feet. They said two adjacent storage caverns carved out of the same salt dome were not ignited and Tidwell said authorities did not consider the fire to threaten them.

Authorities called in experts at capping blown-out wells to examine how to cool down and control the fire at the Duke Energy site.

One leak feeding the flames is apparently located at a flange between a master valve and emergency shut-off, said Guy Grossman, Houston district director of the oil and gas division of the Texas Railroad Commission, which oversees natural gas storage. Another valve that possibly could be used to turn off the flow of gas was too hot to reach.

The cause of the new blast had not been determined.

Moss Bluff (search) is a sparsely populated area about 40 miles northeast of Houston. The area is dotted with manmade caverns inside salt domes, which are the world's largest storage site for explosive hydrocarbons. One underground gas leak in 1980 forced 72 families from their homes in nearby Mont Belvieu (search) for almost five months.