LOS ANGELES (CBSLA.com) — Dense fog blanketed much of the Southland Thursday morning.

According to the National Weather Service, a dense fog advisory will remain in effect until 9 a.m. in the San Fernando and San Gabriel valleys, Los Angeles County beach cities, downtown Los Angeles, the Hollywood Hills, and parts of Ventura and Santa Barbara counties.

READ MORE: Off-Duty Delta Flight Attendant Becomes Unruly, Forcing Plane From LA To Atlanta To Land In Oklahoma City

Forecasters say the fog reduced visibility to a quarter-mile or less, creating dangerous driving conditions along several local freeways, including the 5, 101, and 118 freeways.

READ MORE: Woman, 30, Suffering From Depression Goes Missing In Canyon Country

Motorists were urged to reduce speeds, leave extra space between themselves and vehicles in front of them, use only low beams and give themselves extra time to reach their destinations.

Several flights were delayed at Los Angeles International Airport due to low visibility.

MORE NEWS: Person Struck And Killed By Amtrak Train In North Hollywood

(©2017 CBS Local Media, a division of CBS Radio Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. Wire services contributed to this report.)