They were aboard the C-130 plane when it came down beside a highway intersection near the local airport in the coastal city of Savannah.
The plane belonged to Puerto Rico Air National Guard and was on a training flight, the National Guard said.
Images shared on social media showed wreckage engulfed in flames and black smoke spewing into the sky.
"We've confirmed nine people, consisting of five crew members and four additional passengers" were on board the plane, Puerto Rico National Guard spokesman Maj Paul Dahlen said.
Officials previously said at least five people were thought to have died on board.
Georgia Air National Guard Capt Jeffrey Bezore said the deceased would be named upon notification of their next of kin.
Puerto Rico Governor Ricardo Rossello said that his thoughts were with the families of those involved while he waited for more information.
"They will receive our support and that of the National Guard of Puerto Rico in this process," he added.
In a tweet, US President Donald Trump said he was monitoring the situation.
"Please join me in thoughts and prayers for the victims, their families and the great men and women of the National Guard," he wrote.
One Instagram user, pilotgabe, posted a picture of the scene from the Hilton Head International Airport.
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