The accident occurred around 10:50 a.m. at a house on Byington Road near the Shanks Gap Road intersection in the Stanley Valley community north of Surgoinsville.
Stanley Valley Volunteer Fire Department Chief Stacy Vaughan said the second-story deck broke away from the side of the house and fell to the ground while the side of the deck farthest from the house remained up.
Among the six people on the deck at the time were two children, their parents, the infant and an elderly female.
No names were released as of Monday evening.
Hawkins County Emergency Management Agency Director Gary Murrell, who also responded to the accident, said the infant and the elderly female were the most seriously injured, and both were flown out by Wings Air Rescue in separate helicopters.
Murrell said the elderly female's legs were pinned under the deck, and she suffered a "very serious" leg fracture.
There was no information about the condition of the infant at Vanderbilt as of Monday evening. Rescuers described the child as being "extremely critical."
The two parents and two children were transported by Hawkins County EMS to Holston Valley Medical Center with non-life-threatening injuries.
Vaughan said the collapse likely happened because the wood attaching the deck to the house had rotted.
Murrell said this should serve as a reminder for everyone to inspect the condition of their deck to prevent similar accidents.
The Hawkins County Rescue Squad an Sheriff’s Office assisted at the scene.