Eight crew members were confirmed dead after a B-52 bomber crashed explosively at Edwards Air Force Base in California during a routine test mission on Monday, Air Force officials said.

“It took off and immediately after takeoff burst into flames,” Col. James Hayes, deputy commander at the 412th Test Wing, said at an afternoon news conference. He called the crash “a horrible tragedy” that had claimed the lives of “eight great Americans.”

He said the plane, a B-52 Stratofortress, was supporting a test for a radar modernization program, and its crew included members of the military and civilians, some of them government contractors. Their names were being withheld pending notification of their next of kin.

Local news footage of the aftermath showed an enormous smear of black ash and soot marking the dusty airfield. The firefighters spraying debris with water at the center of the scene looked like miniatures.

The crash took place at around 11:20 a.m. It appeared to spark a large explosion and a fire that created a dark smoke plume visible from far across the scrubby Mojave Desert landscape, according to photos posted to social media by witnesses.

Colonel Hayes said that the cause of the crash was not immediately clear, and that initial fact finding had already begun for what is expected to be a monthslong investigation. He said that emergency crews responded immediately but it was clear that no one could have survived the crash.

Edwards Air Force Base, located in a sparsely populated expanse about 100 miles northeast of Los Angeles, is known as the military’s premier aerospace testing ground, both because of its wide-open geography and because of its proximity to other aerospace hubs in Southern California.

The base, which is 484 square miles, is home to the world’s largest airfield and is where the pilot Chuck Yeager first broke the sound barrier in 1947.

The B-52 aircraft is a high-altitude bomber capable of carrying nuclear weapons. It is also used to surveil large areas of ocean surface. (Two B-52 Stratofortresses can monitor 140,000 square miles of ocean in two hours, according to the Air Force.)

Officials at Fort Hood in Texas on Friday warned nearby residents that a B-52 Stratofortress would be conducting a training that involved the release of 500-pound munitions. Such trainings, Fort Hood officials said, take place “regularly to maintain readiness.” The test in California on Monday, however, appeared to be part of an initiative to bring the equipment into the digital age. Officials said that air operations at Edwards would be temporarily halted as the investigation started.

Lancaster, a city about 40 miles from the base in California’s Antelope Valley, was close enough for the local authorities to reach out to the base to offer assistance, but Mayor R. Rex Parris said the offers were declined.

Mr. Parris, who grew up near the Edwards base in the community of Palmdale, said that when he was a child, planes crashed at the base “all the time.”

“But in the past 30 years, they’ve developed much better safety procedures,” he said. “These days, they have much better safety procedures and these things are very very rare.”

Michael Levenson contributed reporting.