* Saturday likely final day for region's deadly storms

* Storm system type not unusual for April in US South

CHARLESTON, S.C. - Tornadoes tore into the Carolinas on Saturday afternoon as the death toll rose to 18 people from storms across the southern United States over the last three days.

A mechanic at a tire shop in Raleigh, North Carolina, said he took shelter in his truck while co-workers squeezed into an interior room when the storm hit.

"It was one hell of a storm," said Bryan Jackson. "I started to see the roof vibrate and then the roof separated and it was gone."

The area south of downtown Raleigh was littered with snapped telephone poles, downed wires, broken glass and roofing debris.

One storm-related death occurred north of Elizabethtown, North Carolina, according to Bladen County Emergency Services.

Six people were injured when a tornado touched down in Berkeley County, South Carolina, the National Weather Service said.

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The service said some mobile homes collapsed in Lee County, North Carolina, from high winds. Local meteorologists said the storm's intensity was declining as it approached the coast.

At Ray Price Harley-Davidson in Raleigh, some 500 people had left the showroom's spring open house shortly before the storm hit around 4 pm.

"We were very fortunate," said Dave Hushek, a manager at the dealership. "It sounded like a train going by. The wind was going this way and then all the sudden it was going that way."

Storms have torn a path of destruction from Oklahoma on Thursday night through the deep South on Friday and on to the East Coast on Saturday.

'Just The Right Combination'

"This system has clearly had the most intense severe storms of the early spring season," said Corey Mead, a meteorologist with the National Storm Prediction Center.

On Friday seven people died in Alabama, seven in Arkansas and one in Mississippi. Two people were killed on Thursday night when a tornado flattened buildings in Tushka, Oklahoma.

Greg Carbin, meteorologist with the Storm Prediction Center, said Saturday would likely be the final day for the deadly storm system in the region.

He said this type of storm system in the South was not unusual for April, as moist spring air meets the remnants of cold winter air.

"You have just the right combination of ingredients for severe weather," Carbin said. "This is a dangerous time in the southern United States."

Tornado season typically runs from March to early July in the United States, moving from south to north as the year progresses. The storms kill an average of 70 people a year.

The worst US outbreak of tornadoes on record occurred on April 3-4, 1974, when 307 people were killed by 148 twisters in 13 states.

Storms, some severe, also were expected on Saturday from the Florida Panhandle through eastern and southern Georgia, according to weather.com.