SAN DIEGO (CNS) - Wind-stoked flames tore over open swaths of brushy land around BlackMountain today, charring hundreds of acres alongside rural neighborhoods and forcing residential evacuations in communities between 4S Ranch and Fairbanks Ranch.

The blaze, dubbed the Bernardo Fire, erupted for unknown reasons shortly after 10:30 a.m. near Del Norte High School, off Camino San Bernardo and Nighthawk Lane.

As of late afternoon, the flames had blackened at least 400 open acres as it moved to the west amid hot, dry and gusty Santa Ana conditions toward Del Sur, Santa Luz, Fairbanks Ranch and Rancho Santa Fe, according to Cal Fire and sheriff's officials. Crews from an array of area agencies attacked the flames on the ground and aboard air tankers and water-dropping helicopters.

No structural damage or injuries had been reported as of 3 p.m.

In the early afternoon, school administrators began evacuating pupils from Del Sur, Stone Ranch and Willow Grove elementary schools by bus, Poway  UnifiedSchool District officials said. Students at the high school near the point of the fire's origin and at nearby OakValley middle school were directed to remain in their classrooms as a precaution, PUSD spokeswoman Jessica  Wakefield said.

No serious air quality issues were reported at any of the campuses, though the smoke was fairly thick at Del Sur Elementary, she said at midday.

As of 2 p.m., authorities had cleared out residents and closed traffic lanes along Artesian Road, Calle Mayer, Camino del Sur, Deer Ridge Road, Del Sur Court, Entrada de Luz East, Run of the Knolls and San Dieguito Road in the  area of Montien Road, according to San Diego police. Fairbanks Ranch Country Club and areas south of CarmelValley also was evacuated.

Those displaced by the blaze were being directed to shelter facilities at Rancho Bernardo and Torrey Pines high schools.