BIG BEND NATIONAL PARK, Texas (AP) _ The worst fire in the history of Big Bend National Park swelled to more than 600 acres Sunday, fueled by tinder-dry vegetation and fanned by wind blowing through canyons, authorities said.

About 100 campers had been evacuated earlier.

Ninety firefighters from several agencies battled the flames Sunday in the High Chisos mountains in southwest Texas, and spokesman Jim Paxon said three helicopters and 160 more firefighters were expected to arrive from other Western states by Monday.

''It's burning vigorously right now,'' Paxon said. ''It's climbing canyons which act as chimneys. And the temperatures are in the 90s. Luckily, winds are light and blowing the fire back into itself.''

He said the wind at the park was between 5 and 15 mph, but ''with these conditions, if winds pick up we'll really be chasing it. We'll be in deep trouble.''

No injuries were reported, and no structures were in danger, authorities at a fire control center said.

Fire officials had put the fire at 1,200 acres, but a helicopter flight determined it covered 615 acres, Paxon said. He said a hiker had reported the location of the fire line a mile from the actual blaze.

''That actually puts us in better shape, but it's still the largest fire in the park's history and it probably will keep spreading for a couple of days before we get it under control,'' said Paxon.

Officials were concerned about a pair of peregrine falcon nests within 1 1/ 2 miles of the flames. Paxon said the nests, which shelter at least four of the endangered birds, weren't at risk from the flames Sunday but crews would be sent to protect them if the wind shifted.

The 708,221-acre park, about the size of Rhode Island, is mainly desert studded with volcanic projections and includes cliffs lining the Rio Grande. The fire fed on brush and woodland, mostly oak, pine and juniper, officials said.

The blaze was believed to have been set by man, Paxon said. Federal fire investigators were expected to arrive Monday.

The National Weather Service forecast temperatures in the 90s with light wind and no precipitation over the next several days. The park's last rainfall was Feb. 17.

The blaze was the first in the park this year, said park ranger Karen Boucher. Last year there were 27 small brush fires. It had charred more land than any other fire in the 45-year-old park's history.

About 100 campers, mostly college students on spring break, were evacuated from the High Chisos when the blaze was reported by hikers Saturday afternoon.

About 2 1/2 miles north of the fire, the Chisos Mountain Lodge was filled to capacity with more than 140 visitors Sunday, said Kim Alexander, an assistant manager at the lodge.

Alexander said the glow of the fire during the night had appeared over Emory Peak, at 7,830 feet, the highest point in the Chisos range.