According to Riordan, a truck operated by Steve Holland, 59, of West Palm Beach, was heading north in the far-right lane then suddenly veered left and collided with a vehicle driven by Robyn Rattray, 41, of Gainesville.
Riordan called the crash a "heartbreaking event".
The crash happened near Gainesville, according to authorities. Vehicle parts and both of the burned tractor-trailer rigs remained on the interstate.
Five children from Louisiana in the passenger van died as well as the adult male drivers of both trucks. The children ranged in age from 8 to 14. Traffic on Friday morning was still backed up for miles, reports Grace King of member station WUFT. When the semi-truck crossed into the southbound lanes, it crashed with the van and the southbound semi-truck, officials said.
The pregnant woman survived and delivered her baby Thursday night, Cox said in a statement Friday.
Cox said church pastor Eric Descant's 50-year-old wife, Karen, was critically injured and his granddaughter was among the children killed. At least eight other people involved in the pileups were injured, some seriously.
Only the last driver, 61-year-old Mark Houghtaling, also of Gainesville, was physically spared.
The church van packed with children was headed south - with just an hour to go to Walt Disney World - when it got caught in a fiery pileup involving two 18-wheelers.
The dead youngsters had all been in a passenger van. Alachua County Fire Rescue posted a photograph on Facebook showing flames engulfing a truck with a vehicle underneath it. Riordan said FHP is still following its normal protocols.
The highway patrol has scheduled a 10 a.m. news conference to discuss the investigation into the crash.
The highway patrol said it is unknown if any were wearing seatbelts.
Officials said eight patients, some of whom sustained critical injuries, were transported from the scene. Authorities have not why they are treating the deaths as potential homicides. They were in fourth, fifth and eighth grades, Dauzat said.
The aftermath closed part of the highway in both directions, causing massive delays along the busy north-south corridor. It remains unclear if the victims died as a result of the crash or the fire that came after the collision.
Dozens of gallons of spilled diesel fuel fed a giant fire that damaged the roadway itself, according to the AP.
The fire has been extinguished.
At one point, investigators say the Alachua County Sheriff's Office dispatched a helicopter to look for potential victims in the woods off the highway.