COLFAX (CBS SF) — Fire crews were able to make progress containing the River Fire burning near Colfax overnight, raising containment on the wildfire to 30% as of Friday morning officials said.

Cal Fire reported that the wildfire that exploded on Wednesday near the Bear River at the edge of Nevada and Placer counties had stayed at approximately 2,600 acres, the same size it was Thursday night.

Cal Fire Info: River Fire Incident Page | Cal OES Evacuation Info | Nevada County Evacuation Map | Placer County Evacuation Map

Fire crews made good progress working throughout the night to strengthen control lines and defend structures within the interior of the burn. Firefighters were patrolling the perimeter of the fire line to mop up hot spots.

Crews were able to raise containment from 15 percent to 30 percent with cooler temperatures aiding the efforts. A total of 88 structures have been destroyed in the fire.

READ MORE: River Fire Erupts in Nevada and Placer Counties; Thousands Evacuated

Several evacuation orders that were issued on Wednesday when the fire broke out — forcing thousands to flee their homes — remain in effect.

While progress was being made on the River Fire, the air conditions in the area remained hazardous on Friday, with an AQI index of 336 as of late Friday morning. Residents in the area were advised to stay indoors and wear an N95 mask if outside.

It threatened 4,000 structures in total, half of them in Colfax, where the population is only about 2,000. Full containment of the River Fire is now expected by Aug. 14, Cal Fire said.