ALONG THE GUNFLINT TRAIL -- Warning that the Cavity Lake wildfire in the Boundary Waters Canoe Area Wilderness (BWCA) could double in size over the next 10 days, fire officials are continuing to add manpower, technology and experience to the forces arrayed against the flames.

"That's why we're bringing in a lot more power to knock this thing down," said Mike Ferris, a spokesman for the national fire management team that will take over today. "The teams working the fire have done a great job. But with the growing size and complexity of this fire, it's real important to jump in hard."

The fire perimeter grew less than a mile to about 45 square miles Thursday, and low winds are expected to limit the growth again today.

Most of the northern and eastern sides of the fire "are pretty secure now," said Erik Christiansen, fuel specialist with the new fire management team.

At a 10 a.m. briefing for residents and vacationers, he and other officials said the fire will continue to burn south and west, maybe for months.

"Overall, we're pretty optimistic," said new incident commander Mike Lohrey at the meeting.

"But now is not the time to let your guard down. A change in the winds -- today light winds from the NW -- could threaten the gunflint trail at the northern and southern ends of the trail, he said.

So far about 60 campsites in the region have been damaged, some of them destroyed, as the fire spread across the area, officials said earlier in morning.

However, much of the eastern flank of the fire is now just smoldering as it butts against prescribed burns over the past two years designed to protect the 60-mile Gunflint Trail, fire command spokesman Mike Ferris said.

The number of ground crews fighting the blaze -- which had burned 34 square miles as of Thursday morning -- will jump today from five to 10, a total of about 200 firefighters. With new crews and more management and support staff, the overall manpower on the fire could quadruple to 1,000 by the end of next week, Ferris said. There also will be more helicopters fighting the fire within days.

Fire officials didn't do a flyover Thursday night to measure the fire but said it pushed the perimeters a quarter-mile or so in some areas and edged from Cook County into Lake County.

The total area affected by the fire, including the surface area of lakes in its perimeter, was about 44 square miles as of Thursday morning.

Officials put the fire cost at $850,000 as of Wednesday, but said that was sure to grow quickly as more firefighters and equipment are added.

Ferris is part of the national "Type 1" management team that replaces the state-led "Type 2" team.

The national team -- one of only 17 such elite teams in the country -- is specially trained to deal with difficult fires.

This "is the kind of fire we fight -- tough ones," Ferris said.

The Cavity Lake fire has become more complex because its wilderness location makes access difficult. Swelling numbers of crews and aircraft require intense coordination.

The fire is near the Canadian border in the BWCA, just west of the popular Gunflint Trail resort area. "But it's going to spread," John Stegmeir, commander of the firefighting effort until 6 a.m. today, told about 75 area residents at a briefing Thursday morning.