Early signs are emerging of a severe slowdown in the U.S. housing market. New listings have plunged 70% in 12 cities east of San Francisco since the area instituted a shelter-in-place order in mid-March due to the coronavirus pandemic, said Mike DelPrete, a scholar in residence on real-estate technology at the University of Colorado at Boulder, citing data from Red Oak Realty.

New listings usually rise at this time of year, as the spring is the peak season for home sales. In King County, Wash., which includes Seattle, new listings have dropped 56%, Mr. DelPrete said, citing John L. Scott Real Estate. Based on data from the hardest-hit parts of the U.S. and around the world, Mr. DelPrete expects a sharp decline in the number of home sales. “My best guess right now is we could see a drop of up to 50% in the U.S. for 2020 compared to last year,” he said.

Nationwide, pending home sales between March 23 and March 29 fell 42% compared with the same period last year, according to real-estate brokerage Redfin Corp.