The C-130 "Hercules" cargo plane from the Puerto Rico Air National Guard crashed around 11:30 am (1530 GMT) near the Savannah airport.

Footage of the crash showed it falling from the sky then exploding in a fireball.

Officials at first said five crewmembers were killed, but it later emerged that other people were also on board.

"We've confirmed nine people, consisting of five crewmembers and four additional passengers" were on board, Puerto Rico National Guard spokesman Major Paul Dahlen said.

He said the four others were also members of the military.

Dahlen could not immediately confirm all nine had died, but said images of the crash spoke for themselves.

Photographs on Twitter showed the charred wreckage of a plane engulfed in flames and billowing black smoke.

US President Donald Trump tweeted he had been briefed on the incident, and offered his condolences to the families of the victims.

Dahlen said the plane was probably more than 50 years old and was headed to the 309th Aerospace Maintenance Regeneration Group at Davis Monthan Air Force Base -- also known as a boneyard for old planes.

The C-130 had been in Georgia for planned maintenance and was thought to have been in good mechanical condition, he added.

An investigation into the incident is underway.

The US military has been rocked by a string of aviation accidents in recent weeks, including an F-16 crash near Las Vegas last month that killed the pilot.

Just a day earlier, four crew members died when a Marine Corps helicopter crashed while on a routine training mission in Southern California.

And in Djibouti, two incidents triggered the grounding of US military flights.

According to the Military Times, accidents involving the military's manned aircraft rose nearly 40 percent from fiscal years 2013 to 2017.

The publication found the rise coincided with budget cuts from 2013, which impacted training and readiness, as well as heavy wear and tear on aircraft from back-to-back deployments.