The four-member crew ejected safely, officials said.
The plane crashed near Broadus, Mont., the Billings (Mont.) Gazette reported. Emergency crews out of Ellsworth were en route to the crash scene about noon. It wasn't immediately clear what caused the aircraft to encounter trouble, the Rapids City (S.D.) Journal said.
"We are actively working to ensure the safety of the crew members and have sent first responders to secure the scene and work closely with local authorities at the crash site," Col. Kevin Kennedy, 28th Bomb Wing commander, said in a news release. "Right now all of our thoughts and prayers are with the crews and their families."
In 1997, a B-1 bomber out of Ellsworth crashed and killed the four crew members aboard, the Journal said. The aircraft was first introduced in 1986 as the successor to the B-52 bomber.