Marion County Coroner Jerry Richardson told the Associated Press early Wednesday that the van was still underwater.
According to ABC affiliate WPDE, the patients were being transported from Loris Hospital Waccamaw Center for Mental Health to McLeod Health, which runs multiple facilities in the region.
As the van traveled down U.S. 76 - about a half-mile from the Little Pee Dee River, which separates Mullins from the town of Nichols - high water swept away the vehicle.
The deputies made it to the top of the van, where they were rescued by a high-water team. The inmates have not been recovered. At this time, the recovery effort is ongoing, and the transportation vehicle can not be removed due to rising waters and risky conditions.
"We are sorry", Thompson said". "It's come up 2 feet since just last night".
Green's mother declined to speak to a reporter Wednesday but said, "It's just a tragedy".
The South Carolina Law Enforcement Division is reportedly investigating the circumstances surrounding their deaths.
Their names also yielded no records in the Horry County jail and court index systems.
A press release from the Horry County Sheriff's Office said that the van had been carrying two detainees.
"I know for many people this feels like a nightmare that just won't end", he said.
"The two deputies attempted to extricate the persons being transported". "We are fully cooperating with the State Law Enforcement Division to support their investigation of this event".
"I know it was hard to leave home, and it is even harder to wait and wonder whether you even have a home to go back to", Govenor Roy Cooper said.
The incident happened in the area of the Little Pee Dee River, which branches off from the Lumber River, in Mullins, South Carolina. It could have been water pressure or the way the van was resting against a guard rail, he said. In March, Christopher Bennett died after eating drugs and suffering medical issues, a SLED investigation found. First responders decided not to continue rescue operations at the scene because of the conditions, Thompson said.