ATLANTA — At least 16 people were believed dead after a military plane crashed in the Mississippi Delta on Monday, prompting an urgent rescue effort in one of the South’s most rural regions, the authorities said.

Fred Randle, the emergency management director in Leflore County, Miss., said in a brief interview late Monday that officials thought at least 16 people had died in the crash. The fire chief in Greenwood, Marcus Banks, said only that there were “multiple fatalities” in the episode, which occurred around 4 p.m. in Leflore County, north of Jackson.

A Marine Corps spokeswoman at the Pentagon, Capt. Sarah Burns, said that one of the service’s KC-130 aircraft had “experienced a mishap.” The Marines, who use KC-130s for aerial refueling, did not immediately provide any additional information, including the plane’s scheduled route.

The cause of the crash, in an unincorporated part of Leflore County, was not immediately clear, but Chief Banks said witnesses described the plane as disintegrating in the air as it neared the ground. The chief estimated that the debris field was about three miles in diameter.

The chief, who said the Fire Department used about 9,000 gallons of foam to extinguish a blaze, said he believed the cockpit and fuselage had fallen about a mile from one of the plane’s wings.

Edna Beavers was trimming the grass outside her house in Itta Bena, Miss., on Monday afternoon when, she said, she glanced up and saw a huge plume of black smoke rising from a soybean field about a mile away. “I was like, ‘Oh my God,’” Ms. Beavers, 68, said in an interview Monday night.

Ms. Beavers said the military plane crashed along County Road 547, a dirt road that connects acres of farmland between Itta Bena and Moorhead. There are few homes along the road, she said. A military jet later circled overhead, she said.

Military aircraft are a common sight in the skies of rural Mississippi, their jet engines reverberating over miles of farmland. But Ms. Beavers said she did not hear the plane fly overhead or hear it crash. As the sun set, smoke was still billowing from the fields, she said.

“That is a sad situation there,” she said.

Mayor Carolyn McAdams of Greenwood, the county seat, said military officials were traveling to the crash scene on Monday night. The Federal Aviation Administration and the Mississippi Emergency Management Agency referred questions to the military.

The F.B.I. was also sending employees to the scene, but a spokesman for the bureau, Brett Carr, said the authorities did not believe foul play was to blame for the crash.

“We’re just trying to offer any type of assistance,” said Mr. Carr, a spokesman for the bureau’s office in Jackson, Miss. “It could be anything from manpower to evidence response.”

Gov. Phil Bryant of Mississippi expressed his condolences after the crash.

“Please join Deborah and me in praying for those hurting after this tragedy,” Mr. Bryant said in a statement, referring to his wife. “Our men and women in uniform risk themselves every day to secure our freedom.”