A vehicle gained "unauthorized access" to Travis Air Force Base in California and exploded, killing the driver, base officials confirmed Thursday.
The vehicle crashed at about 7 p.m. (10 p.m. ET) Wednesday at the main gate of the base, near Fairfield in Solano County about 30 miles southeast of Sacramento, officials said. The driver, who was not publicly identified, was pronounced dead at the scene as explosive-ordnance crews and Fairfield emergency officials responded.
The base, which employs more than 26,000 active-duty, reserve and civilian employees, said Thursday that the scene had been declared safe and that the gate was open, but it gave no further information.
Fairfield police Lt. Greg Hurlbut, whose agency assisted with the initial response, called it "a unique and unusual situation."
Hurlbut told NBC News that the base's ordnance disposal personnel initially warned people on the scene of the possibility that a bomb was involved, but later declared the area safe after a robot was dispatched to check the vehicle out.
The FBI responded to the scene at about midnight, Hurlbut said. The FBI's Sacramento office didn't immediately respond to a request for comment.
Videos posted on a Facebook forum for members of the Air Force show a dark truck or sport utility vehicle in flames inside the gate with thick gray smoke billowing into the sky.
An account from an apparent witness on the forum said the vehicle was carrying propane tanks when it approached the gate. The driver "started messing with a fuel ignition source to blow the propane tanks" before driving to the side of the road, "where he burned to death," according to the account.
"We didn't know if it was a terrorist attack or a suicide, but we were using the word bomb for the incident," according to the account, which said no shots were fired.
NBC News hasn't verified the authenticity of the video or the Facebook accounts. The page is a well-established forum widely used by airmen and noncommissioned officers, and its contents are moderated.
The main gate at Travis is near the base's family military RV park. The base closed access to the camp overnight as it investigated and reopened it at 8 a.m. Thursday.