U.S. authorities say all four airmen aboard a plane that crashed at an air force base in Alaska were killed.

A plume of smoke is seen after a plane crashes on the Elmendorf Air Force Base in Anchorage, Alaska, on Wednesday evening. (Roger Herrera/Associated Press)

Three of the men were in the Alaska Air National Guard, while the fourth was on active duty at Elmendorf Air Force Base, Col. John McMullen said Thursday. The men's names have not been released pending notification of relatives.

The plane was on a local training run Wednesday when it crashed at the base, near downtown Anchorage. Witnesses said the crash sent a fireball about 250 metres into the air.

Anchorage Fire Dept. Captain Bryan Grella said his crew was just finishing dinner at about 6:30 p.m. at the downtown fire station when something caught his eye.

"It was a big, grey plume of smoke, and I saw a fireball go up in it," he said.

The military said it would investigate the crash.

The crash is the third airplane incident in Anchorage this summer. In June, one child was killed and four others burned when a small plane crashed after taking off from the city's small-airplane airport in downtown Anchorage.

Days later, a small plane landed on the busy Glenn Highway, the only highway leading north out of Anchorage. There were no injuries in the latter mishap.

Gov. Sean Parnell and Senator Mark Begich issued statements late Wednesday expressing sadness over the crash and sending condolences to members of the military.