Tennessee Emergency Management Agency spokesman Jeremy Heidt in Nashville said the flight crashed near Brownsville during a rainstorm shortly after 6 a.m. CDT.
Heidt said the helicopter had flown a patient from Parsons to Jackson-Madison County General Hospital and was returning to its base in Brownsville when it went down only a few miles from its destination. All those aboard were crew members.
Rich Okulski, a supervisor in the Memphis office of the National Weather Service, said the agency doesn't have an observer in Brownsville, but said his office has submitted a report to NWS officials that weather could have played a role in the crash.
Okulski said at the time of the crash, a thunderstorm was in progress at McKellar-Sipes Regional Airport in Jackson, about 25 miles east of Brownsville and a line of thunderstorms had cleared Memphis, about 55 miles southwest.
A photograph from the scene by WNWS radio in Jackson shows charred wreckage of the craft in what was described as a wheat field.
The flight was operated by Hospital Wing, a nonprofit air medical transport service with headquarters in Memphis.
"Nothing like this has ever happened in our history," Allen Burnette, program director and chief operating officer, told WMC-TV.
The company's Web site says it flies the Eurocopter Astar AS350B3 model, which is capable of carrying a three-person crew and one patient.
Hospital Wing has three bases. The one in Brownsville opened in 2004 serving 26 counties in Tennessee, Mississippi and Arkansas, the Web site says.
The crash scene is near U.S. 70 and about 55 miles northeast of Memphis.
