Kentucky State Police said the explosion was reported around 9am on Friday and that there was no early indication of foul play in the incident.
Of those, at least six people were taken to area hospitals and two of those were airlifted. There were 41 people present on site, but not all of them were on the boat at the time of the explosion.
Autopsies were scheduled for the victims.
Two Louisiana men were among those killed when a tugboat exploded Friday morning on the Tennessee River in Kentucky, officials said.
Javier Fuenes, 21, was transported by ambulance to Marshall County Hospital for treatment of minor injuries.
The explosion was on a commercial vessel associated with Western Rivers First Marine. The nature of the work was not specified.
Cash called the coordination between the multiple law enforcement, fire, rescue and medical agencies "seamless".
Emergency responders are on the scene of a deadly tug boat explosion in Western Kentucky.
Kentucky State Police say that an investigation revealed that the explosion happened inside the boat which was being worked on.
Because the boat was considered to be dry docked and not out on the river, the U.S. Coast Guard did not take over the investigation.
Three people - 52-year-old Timothy Wright of Calvert City; 56-year-old Jerome Smith of Thibodaux, Louisiana; and 41-year-old Quentin Stewart of Opelousas, Louisiana - were pronounced dead at the scene by the Marshall County coroner.
This story will be updated.