MOSS BLUFF, Texas (AP) - A second explosion in less than 24 hours rocked a burning underground gas storage facility early today, prompting authorities to expand an evacuation zone around the site.

The fire at Duke Energy's Moss Bluff natural gas facility, 40 miles northeast of Houston, 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.

No injuries were reported.

Authorities had decided to let the fire ignited in the first explosion Thursday burn itself out, a process they said would take several days. The explosion was blamed on leaking gas.

The second explosion this morning happened because the fire caused a valve to give way on top of the storage cavern, said Danny Gibbs, a spokesman for Charlotte, N.C.-based Duke Energy.

Everyone within a three-mile radius of the facility was being evacuated, and additional shelters were being set up, authorities said. The first explosion had prompted evacuations within a one-mile radius in the sparsely populated area.

Authorities called in experts at capping blown-out wells to examine how to cool down and control the fire. The first blast about 4 a.m. Thursday sent flames 150 to 200 feet into the air. An employee making his rounds at the time escaped unharmed, said sheriff's Capt. Bill Tidwell.

Workers shut off the supply of gas feeding the underground storage cavern, which holds 6 billion cubic feet.

They said two adjacent storage caverns were not ignited and Tidwell said authorities did not consider the fire a threat to them.

Moss Bluff 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 for almost five months.