Jamboree spokesman Gregg Shields said the accident occurred between 4:30 and 5 p.m. while the leaders were setting up camp.
One other leader and a contract worker were injured, and were hospitalized in stable condition, Shields said. No youth Scouts were seriously hurt, he said. He did not say how many might have sustained minor injuries.
Shields did not have additional details about the accident, including the victims' names.
"We have an investigation under way," he said.
More than 40,000 Boy Scouts, leaders and volunteers from around the world are attending the 2005 National Scout Jamboree. The event Monday at the Army's Fort AP Hill, a 76,000-acre Army training base about an hour south of the nation's capital.
The Jamboree runs through Aug. 3 with President Bush scheduled to speak Wednesday evening. Scouts ages 12-18 are to spend 10 days camping in tents and doing activities that include archery, fishing and a GPS-based scavenger hunt.
The Boy Scouts of America have held the event since 1937 with the next gathering set for 2010, the Scouts' 100th anniversary.