Final update: One of the region’s major commuter arteries was shut down for hours Monday after a high-pressure natural gas main was accidentally ruptured, authorities said.

Several miles of Interstate 270 were closed in both directions in upper Montgomery County after the 4 p.m. construction accident in the Clarksburg area.

Washington Gas lowered pressure in the eight-inch main so that repairs could be made, county Assistant Fire Chief Scott Graham said. The road reopened shortly after 10 p.m.

The main was about 25 feet underground at the ramp from northbound 270 to eastbound Route 121. It broke as pilings were being sunk for the early stages of repairs to a parallel main, Graham said.

The force of escaping gas shattered the windshield of a piece of construction equipment nearby, he said. A cloud of earth continued to rise from the site late Monday.

Traffic backed up on surrounding county roads, police said.

No injuries were reported.

Another gas line was cut nearby Monday in an unrelated incident.

— Martin Weil

6:20 p.m. Update: The Maryland State Highway Administration is estimating that I-270 could be closed up to six more hours. Officials were investigating reports of a possible second leak.

Original post: A broken gas main in Clarksburg has led to the closure of Interstate 270 and Clarksburg Road, according to Montgomery County police.

Montgomery County officials said a construction crew struck the main.

I-270 southbound is closed at Route 109; I-270 northbound is closed at Route 118 (Germantown Road), police said.

Clarksburg Road is shut down in both directions between I-270 and Route 355, authorities said.