Wind helped a northwestern Montana wildfire expand to about 6,000 acres as crews labored to protect homes and a power line that serves a microwave tower.

The latest estimate of the Seepay 2 fire's size reflects both growth of the blaze and some clearing of smoke that hindered earlier measurement, information officer Wayne Johnson said Wednesday. On Tuesday, the fire east of Plains was estimated at 3,300 acres.

Montana 200 was open to traffic Wednesday after smoke a day before limited visibility and closed the highway intermittently.

The fire is about 15 miles east of Plains, on the edge of the Flathead Indian Reservation.

Johnson said there had been no evacuations, but ‘‘pre-evacuation notices'' were issued and ‘‘some folks chose to leave and some chose to stay.'' The fire threatened five homes, he said.

It burned entirely out of control early Wednesday. No rain was in the weather forecast and firefighters braced for more wind after gusts to 30 mph the night before.

Human activity is believed to have started the fire, and an investigation is ongoing, Johnson said. The blaze, reported Sunday, was burning trees, brush and grass.

Besides protecting homes and the microwave tower's power line, the crews are trying to keep the fire out of an area with a large volume of dead lodgepole pine trees, Johnson said.

Nearly 240 people were assigned to the blaze.