Two female mental health patients drowned in the back of a sheriff's van in South Carolina when the vehicle was overcome with floodwaters, according to authorities.

"Tonight's incident is a tragedy," Horry County Sheriff Phillip Thompson said in a statement, ABC News reports. "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."

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ABC News also reported that the deputies, who were transporting the two women to another facility in South Carolina, were saved after rescue teams arrived in time to save them.

The two deputies transporting the women attempted to pull them to safety, according to Thompson's statement, but could not open the doors to reach them, given how rapidly the water rose.

The two women, being shackled in the car, could not extricate themselves.

Neither patient has been identified, though the coroner in a neighboring county has confirmed they were female.

The deputies were transporting the women to Loris Hospital Waccamaw Center for Mental Health to McLeod Health when the floodwaters overcame the van, according to ABC affiliate WPDE.