A massive chain‑reaction crash involving as many as 150 vehicles shut down both directions of Highway 99 in Central California on Saturday morning, trapping drivers in near‑zero visibility and sending at least 10 people to area hospitals as dense tule fog once again smothered the San Joaquin Valley.

The California Highway Patrol began receiving panicked calls from motorists near Earlimart, California, shortly after 8:15 a.m., reporting multiple collisions on both the northbound and southbound lanes near Avenue 24. Officials say visibility at the time of the crash was 100 to 200 feet — the type of conditions CHP frequently describes as “sudden wall of white” events.

“Drivers were hitting fog so thick they couldn’t see brake lights until it was too late,” authorities said.

Dozens of drivers who escaped injury were taken by bus to the Tulare Ag Center for shelter and reunification. As of 1 p.m., Highway 99 remained fully closed, and officials said the shutdown could last well into the evening while officers investigate and tow trucks work through the tangled stretch of crumpled cars, SUVs, and big rigs.

Here's what to know about the tule fog blanketing California's Central Valley and the rash of accidents that fog has caused this season.