Two female patients at a mental health facility drowned after they became trapped in a police van as it was overcome by floodwaters in South Carolina, authorities said.

Deputies with the Horry County Sheriff’s Office were transporting the two women, who have not been identified, to another facility on Highway 76 when they hit rapidly rising floodwaters, Sheriff Phillip Thompson said in a statement. 

The women, who were shackled, became trapped inside the vehicle. 

"Despite persistent and ongoing efforts, floodwater rose rapidly and the deputies were unable to open the doors to reach the individuals inside the van," Thompson said.

Rescue teams were able to get to the deputies, authorities said. 

"Tonight's incident is a tragedy,” Thompson said in the statement. "Just like you, we have questions we want answered."

The South Carolina State Law Enforcement Division is investigating the incident. 

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