The National Weather Service issued a tornado warning for portions of four counties south of the Sacramento area Thursday afternoon.
The warning for northeastern San Joaquin County, northern Stanislaus County, west central Calaveras County and southwestern Amador County was initially in place until 5:15 p.m. but then extended until 6 p.m., the weather service said.
“At 4:35 p.m., a severe thunderstorm capable of producing a tornado was located near Rancho Calaveras … moving at 15 mph,” the weather service said.
Weather service radars picked up “very strong rotation,” which could indicate a tornado, forecasters said.
“Flying debris will be dangerous to those caught without shelter,” forecasters said. “Damage to roofs, windows, and vehicles will occur. Tree damage is likely.”
Authorities urged residents to seek shelter.
This story is developing and will be updated when more information is available.