UPDATE 6-South Carolina orders 1 million to evacuate ahead of Florence

* Could make landfall in Carolinas on Thursday

North Carolina governor says entire state may be impacted

* Inland flooding expected to be intense (Adds South Carolina evacuation order)

By Anna Driver

HOLDEN BEACH, N.C., Sept 10 (Reuters) - South Carolina on Monday ordered an estimated 1 million people to evacuate its coast as the state and neighboring North Carolina brace for a hit from Hurricane Florence, the most powerful storm to take aim at the U.S. mainland this year.

The storm had winds of 130 miles per hour (209 kph) and was due to gain strength before making landfall, which the U.S. National Hurricane Center said was likely to occur early Thursday, bringing heavy rain that could cause severe flooding through the region.

"We do not want to risk one South Carolina life in this hurricane," Governor Henry McMaster said at a news conference.

He estimated about 1 million people would be fleeing the coast.

In North Carolina, officials already had ordered some 250,000 residents and visitors to begin evacuating the Outer Banks barrier islands.

"We are in the bull's eye," North Carolina Governor Roy Cooper said at a news conference. "This is going to be a statewide event."

By 11 a.m. ET (1500 GMT) on Monday, Florence was about 1,240 miles (2,000 km) east-southeast of Cape Fear, North Carolina, and was a Category 4, the second-strongest on the Saffir-Simpson scale, the NHC said.

(Additional reporting by Roberta Rampton and Idrees Ali in Washington, D.C., Gene Cherry in Raleigh, N.C. and Rich McKay in Atlanta, writing by Bernie Woodall; Editing by Scott Malone, Bill Trott and Nick Zieminski)