The two women have not yet been identified.
ABC News reports that the van was traveling on Highway 76 when it was overtaken by severe flooding.
In a statement, Horry County Sheriff Phillip Thompson called the deaths a "tragedy", while noting that the two deputies have been placed on administrative leave. 'Just like you, we have questions we want answered'. "We are fully cooperating with the State Law Enforcement Division to support their investigation of this event".
There are widespread road closures due to flooding on primary and secondary routes throughout the Pee Dee, according to the SCDOT.
Forecasters predict some rivers in the northeastern area of the state might not reach their highest levels until later this week or next week.
In North Carolina, transportation officials Tuesday continued advising motorists who ordinarily might take southbound I-95 from Virginia to SC that flooding has made long sections of I-95 in North Carolina impassable.
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Though in this case, it's possible Florence isn't to blame so much as the officers transporting the two women and the department that waited so long to relocate them.
"I know that it is a very sad situation so ive just been praying for the victims and the families of the victims", said Martin.
President Donald Trump, meanwhile, arrived in storm-ravaged North Carolina on Wednesday and helped volunteers at a church in the hard-hit coastal town of New Bern. "Right now, everybody is saying what a great job we are doing with Hurricane Florence - and they are 100% correct", he tweeted.
Horry County referred all questions about the incident - including whether the women had been locked up or were merely being transported - to state investigators, who said they had no new information to release.
Officials said that the van was near the Little Pee Dee River, one of the bodies of water that state officials are watching following the heavy rains of Florence.
"The two deputies attempted to extricate the persons being transported". "Floodwater rose rapidly and the deputies were unable to open the doors to reach the individuals in the van".
Rescue teams were able to get to the deputies, authorities said.
Richardson said the van came across rising water and was carried off the road. In March, Christopher Bennett died after eating drugs and suffering medical issues, a SLED investigation found.