South Carolina's forest fire chief said that a yard debris burn started the massive wildfire that has destroyed 70 homes and damaged 100 others over the past three days.

The state's worst wildfire in at least three decades, the blaze threatened to intensify Friday after a lull overnight, when calm winds and firebreaks helped contain the blaze that demolished homes and roared through woods just miles from the most-populated stretch of the state's tourist beaches.

Accelerating winds were expected to feed hotspots and push the fire that has consumed 31 square miles farther northward away from the undamaged tourist strip, forestry and county officials said.

County officials on Friday morning put early damage estimates at nearly $8.3 million. No injuries have been reported.

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About 30 firefighters manned containment lines overnight and were able to reinforce some of them, Welch said.

She said the blaze was about 50 percent contained early Friday but noted the picture could darken with the slightest change in the weather. Winds blowing inland from the Atlantic coast have been feeding the fire and pushing it north.

"Where we think we have things secured, that could all go out the window," she said.

Horry County Public Safety director Paul Whitten said he expected hot spots to flame up Friday as winds increase. The National Weather Service said winds could reach speeds close to 15 mph by the afternoon, with some higher gusts.

The fire started several miles inland Wednesday and has cut a path four miles wide through tinder-dry scrubland but skipped its way through housing developments, decimating some homes while leaving their neighbors untouched.

That's not unusual because the fire's embers can travel far distances before landing to create blazes of their own, said Mike Bocco, the state Forestry Commission official overseeing the fight.

"A lot of times, the big, raging fire that burns through a forest is not what actually burns the homes down," he said. "The wind is picking up those embers, blowing them several hundred yards into the lawns, into the pine straw mulch, around the homes, landing in that straw, igniting, and burning the house down."

The fire started near subdivisions and golf courses that have been carved from forest and swamps over decades. On Thursday, state forestry officials said they issued two citations to someone for starting a fire that got out of control, but it was unclear whether that person had started the massive blaze.

The fire got within 1 1/2 miles of Route 17, the main coastal road that links beachfront towns and is lined with fast-food restaurants, beachwear stores and trinket shops. By Thursday evening, the flames were about 3 miles west of the highway, a distance Bocco said he hoped to maintain Friday with intensive prevention work already completed to the north.

"We've got a good line up ahead of that right now, and hopefully we can contain it there, and the winds won't give us a problem as far as blowing embers across the water," Bocco said.

A day after some people from a golf course development hit the hardest by the damage returned to their homes, others waited to get back in.

"I haven't seen it and I'm still not sure," said Ann Tootham, 60. "I won't believe anything until I've seen it with my own eyes."

The blaze has headed away from the high-rise hotels that line Myrtle Beach, which anchors the state's $16 billion annual tourist industry. College students are drawn here for a cheap spring break destination, and families fill miles of budget hotels in the summer.

On Thursday, a column of smoke rose on the inland side of the Intracoastal Waterway, a canal as wide as a football field that separates the city's main drag from homes. At times the smoke seemed to block out the sun, casting an orange sheen on the vehicles of motorists slowing to gawk at the scene.

Just a few miles south along the coast, people were unaffected. Golfers kept their tee times and tourists spread out on the beaches. Hotel managers, who offered vouchers to the evacuees, said they could not even smell the smoke.

As ash fell, the governor issued a state of emergency, and schools closed early. But North Myrtle Beach Mayor Marilyn Hatley managed to promote the area while announcing the number of homes destroyed.

"Certainly come on to the Grand Strand area and enjoy yourself," Hatley said.