The two deputies inside the van were rescued, however.
The two deputies attempted to "extricate the persons being transported," the sheriff's office said in a statement.
The women, Windy Newton, 45, and Nicolette Green, 43, were "still under the water," Marion County Coroner Jerry Richardson told the Associated Press on Wednesday morning. The waters were still apparently rising then. As of Wednesday afternoon, their bodies were still locked in the vehicle.
The vehicle was carried off the road by flooding, according to the coroner.
"Despite persistent and ongoing efforts, floodwater rose rapidly, and the deputies were unable to open the doors to reach the individuals inside the van," the sheriff's office's said in a statement.
It isn't clear why the deputies were rescued and the women were not; however, the law enforcement officers were in the front section of the vehicle, which has doors on either side, while the back section where the women were has only one access point.
"Just like you, we have questions we want answered," Horry County Sheriff Philip Thompson said on Wednesday, calling the deaths a "tragedy."
State Representative Justin Bamberg, who has worked as an attorney for people injured or killed by police, said the women should not have been transported during floods. A court order had been issued for their transportation.
"If that road is in an area where it is a flood risk, why were they driving on that road anyway?" Bamberg asked. "People need to know exactly how it happened," he added, according to AP. "It makes it seem like someone took a very unnecessary risk."