Originally Published: 11 JUL 23 10:37 ET

By Dakin Andone, CNN

(CNN) — A dozen homes have been evacuated in Rolling Hills Estates, California, after the ground shifted, causing extensive damage, city and Los Angeles County officials said.

Twelve homes were red-tagged as of Monday night, the Los Angeles County Fire Department said on Twitter, noting 10 were “actively moving.” Sixteen residents had been displaced, and the fire department is monitoring another 16.

The incident has been unfolding since Saturday, with footage from CNN affiliate KCAL showing homes crumbling on the hillside, the structures buckling as the earth gives way. And there’s no clear indication when the ground movement might end.

“They’ve moved almost 20 feet since last night, and homes that I saw last night are now gone,” L.A. County Supervisor Janice Hahn said Monday, according to KCAL.

“They have already fallen into the ravine,” Hahn, whose district includes Rolling Hills Estates, said of the affected homes Monday on Instagram. “We’ve got back decks that are gone. We’ve got roofs that are at eye level with the driveway. I’ve never seen anything like it. They’re completely uninhabitable.”

Officials learned of the “significant land movement” along Peartree Lane on Saturday, according to an update on the city’s website. Rolling Hills Estates is a largely residential city on the Palos Verdes Peninsula, just west of Long Beach and about 30 miles south of Los Angeles.

Fire department units have been on the scene since 1:30 p.m. that day, when they identified cracks or the beginning of cracks in the foundations of 12 homes, Chief Anthony Marone of L.A. County Fire said at a news conference Monday. Since then, Marone said, 10 homes “have been lost.”

Personnel from the county fire department and the Los Angeles County Sheriff’s Office will remain “until this situation is eventually mitigated,” Marone said. “And we don’t know how long that’s going to take. We don’t know how long these homes are going to continue to move.”

The cause remains unclear. Hahn told reporters it was up to the homeowner’s association to hire a geologist or soil expert to discern the cause. But she theorized on Instagram that periods of heavy rain after a drought had created a ground fissure that caused the land to shift.

Affected residents met officials at City Hall on Monday, Rolling Hills Estates Mayor Britt Huff said.

Los Angeles County Assessor Jeff Prang said the property owners would be entitled to property tax relief.

Rolling Hills Estates, with a population of about 8,000, has a median household income of about $160,000, according to data from the US Census Bureau.