At least 16 people have died in the US state of Arkansas after floodwaters hit campsites in a mountainous national park, state governor Mike Beebe says.

Two dozen people were taken to hospital and some 30 others remained unaccounted for.

Helicopters are taking part in the search in a remote, mountainous area in the state's south-west.

The operation is focused on campsites along the Little Missouri and Caddo rivers in the Ouchita Mountains.

Mr Beebe said the deaths had occurred at about 0530, when the floodwaters reached their peak.

A river gauge at Langley, just south of Albert Pike in the Ouachita National Forest, showed the water rose 8ft (2.4m) in one hour, according to the US Geological Survey.

The National Weather Service said 7.6in (19.3cm) of rain had fallen overnight.

Some campers described how they had to cling to trees for hours to survive.

The remains of destroyed tents and damaged log cabins were later seen lining the banks of the swollen rivers.

The governor said damage to the area was comparable to a strong tornado.

'People trapped'

Police spokesman Bill Sadler told US network CNN: "We believe there are still individuals trapped in the area.

Image caption Some campers later said they had to cling to trees for hours to survive raging torrents pouring through the campsites. It [pick-up truck] was just like a boat tied to a tree Marc Marshall, Survivor In pictures: Arkansas floodwaters

"The primary mission of the Arkansas state police working with the local authorities right now is to get the living out of that area and locate the dead."

Officials were bringing in a refrigerated truck to act as a temporary morgue, he said.

The authorities warned that it could take days to find survivors or recover bodies because of the rugged terrain.

Police originally put the death toll at 12 and later updated it to 20, but the governor's office said the higher figure had been based on an erroneous figure from a rescue worker.

It is not clear whether all those killed were staying at the campsites washed away by the floodwaters.

Brigette Williams, of the American Red Cross in the state capital Little Rock, said between 200 and 300 people were believed to be in the area at the time but it was unclear how many were campers and how many local residents.

Rescue worker Gary Fox said the Albert Pike Recreation Area, a 54-unit campsite in the national forest, was packed with families on holiday when the floodwaters hit.

More than 20 people were taken to hospital and another 60 were rescued from the steep Ouachita Mountains valley.

The region includes a mix of campsites, hunting grounds and private homes.

Marc and Stacy McNeil of Marshall, Texas, survived by hauling their pick-up truck between two trees and standing in waist-deep water.

"It was just like a boat tied to a tree," Mr McNeil said, describing how the truck bobbed up and down.

They said the water kept rising throughout the night. By dawn the rain stopped, the water receded and they were able to walk to safety.

National Guard troops are helping to look for those affected.