By Joseph J. Kolb

ALBUQUERQUE N.M. (Reuters) - A wind-driven wildfire raged unchecked for a sixth day through parched pine woodlands and brush on a Navajo reservation in northwestern New Mexico on Wednesday, threatening dozens of homes after destroying about 11 dwellings, officials said.

The Assayii Lake fire has charred more than 13,000 acres (5,261 hectares) since it erupted last Friday in the Chuska Mountains, about 6 miles (10 km) east of the Arizona border, and spread eastward toward the communities of Sheep Springs and Naschitti.

The fire is believed to have been human-caused and as of Wednesday remained at zero-percent containment, despite the efforts of nearly 700 firefighters backed by nine water-dropping helicopters, fire managers said.

Estimated property losses include 11 homes and prime grazing areas that are key to the livelihoods of the reservation's sheep-herding residents.

The blaze was threatening about 50 more homes in Sheep Springs and Naschitti along U.S. Highway 491. Residents were advised to be ready to evacuate at a moment's notice.

New Mexico Governor Susana Martinez surveyed the fire zone by air on Tuesday and said state authorities were monitoring the blaze to ensure that firefighters and affected communities have the resources they need.

Winds gusting to 50 miles per hour (80 kph) have thwarted efforts to contain the blaze for days but Charlie Armiger, a spokesman for the fire command center, said firefighters may soon get a break from a change in the weather.

"The winds have shifted and have died down and the fire is now approaching light-fuel areas, slowing its progress," he said on Wednesday.

On Monday, Navajo Nation President Ben Shelly declared a state of emergency, seeking federal disaster assistance.

The Navajo Nation, the largest Native American reservation in the United States, occupies more than 27,000 square miles, an area roughly the land mass of West Virginia. The bulk of the reservation spans the northeastern corner of Arizona, but about a third lies in northwestern New Mexico and southeastern Utah.


(Editing by Bill Trott)