Two mental health patients have died when the police van they were being transported in got caught in floodwaters in the US, police say.

The two officers escorting the pair were eventually rescued. The patients' deaths bring the death toll from Storm Florence to 37.

Thousands of homes and roadways in the region remain underwater less than a week after the storm made landfall.

President Donald Trump arrived in North Carolina on Wednesday to survey damage.

Mr Trump praised the response to the "devastating" storm by federal and local disaster officials at a news conference in North Carolina on Wednesday morning.

"Unfortunately, the money will be a lot, but it's going to come as fast as you need it," Mr Trump said. "We're going to take care of everybody."

Mr Trump will be heading to South Carolina next.

The storm's latest victims in South Carolina were identified as Wendy Wenton, 45, and Nicolette Green, 43, by the Marion County Coroner, US media report.

The Horry County Sheriff's Department said in a statement that when the waters overtook the van, they rose too quickly for the pair to be saved.

A high water team eventually rescued the two deputies who were escorting them. The deputies were able to climb atop the van as waters inundated the vehicle.

The detainees were women being transported from Waccamaw Mental Health and Loris Hospital to a behavioural health hospital in Darlington, South Carolina, according to the Associated Press.

"Tonight's incident is a tragedy," Sheriff Phillip Thompson told the Greenville News.

"Just like you, we have questions we want answered. We are fully co-operating with the State Law Enforcement Division to support their investigation of this event."

The tragic incident occurred near the Little Pee Dee River, which continues to rise as water from upriver North Carolina makes its way into South Carolina's waterways. (BBC)

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