HELENA, Ala. — A fatal explosion has shut down a pipeline supplying gasoline to millions of people across the Southeast — the second accident and shutdown in two months — raising the specter of another round of gas shortages and price increases.

It happened when a dirt-moving track hoe struck the pipeline, ignited gasoline and sparked a blast Monday, killing one worker and injuring five others, Colonial Pipeline said. Flames and thick black smoke continued to soar on Tuesday, and firefighters built an earthen berm to contain the burning fuel.

The explosion happened not far from where a pipeline sprung a leak and spilled 252,000 to 336,000 gallons of gasoline in September. After the leak, the company was able to use one of its two main lines to move fuel through as it made repairs, but it still led to days of dry pumps and higher gas prices in Alabama, Georgia, Tennessee and the Carolinas while repairs were made.

Fuel shortages in the Southeast could be more severe this time if both of Colonial Pipeline's main lines remain shut down, as they were Tuesday, for several days, experts say. Together the two pipelines carry more than 2 million barrels of fuel a day.

"Both lines are down, no gasoline is moving down the line. Nothing is going through," said Tamra Johnson, a spokeswoman for AAA. "So we can actually start seeing some supply outages in the coming days if they don't put a plan in place."

If the pipeline's two main lines remain closed, motorists could begin seeing prices rise at the pumps within about a week, Johnson said.

After the explosion, gasoline futures rocketed almost 8 percent higher on the New York Mercantile exchange, to $1.53 per gallon.

"In a worst-case scenario we could be talking about more severe outages than what we saw back in September. It's very worrisome that both pipelines are shut down right now," said Patrick DeHaan, an analyst with price-tracking service GasBuddy.com.

The severity of the situation will depend on how long the pipeline remains closed — whether it's a few days or a few weeks, AAA spokesman Mark Jenkins said.

The cause of the September leak still has not been determined.

Colonial Pipeline, based in Alpharetta, Georgia, operates 5,599 miles of pipelines, transporting gasoline, jet fuel, home heating oil and other hazardous liquids daily in 13 states and the District of Columbia, according to company filings.

Plagued by a severe drought after weeks without rain, the section of Alabama where the explosion happened has been scarred by multiple wildfires in recent weeks, and crews worked to keep the blaze from spreading.

Coleen Vansant, a spokeswoman with the Alabama Forestry Commission, said crews built a 75-foot-long earthen dam to contain burning fuel. The Shelby County Sheriff's Office said the blaze had been contained but it was unclear how long the fire may take to burn out.

Two wildfires caused by the explosion burned 31 acres of land, Vansant said.

"We'll just hope and pray for the best," Gov. Robert Bentley said in a statement.

Houses around the blast scene were evacuated, and sheriff's Capt. Jeff Hartley said it wasn't clear when people might be able to return home.

Eight or nine subcontractors were working on the pipeline when it exploded about 3 p.m. Monday, sheriff's Maj. Ken Burchfield told Al.com. The conditions of those hurt weren't immediately known.

"Colonial's top priorities are the health and safety of the work crew on site and protection of the public," the company said in a brief statement.

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Associated Press Writer David Koenig in Dallas contributed. Jay Reeves reported from Helena, Alabama; Jeff Martin reported from Atlanta.