The "Safer at Home" order calls for nonessential businesses to cease operations that require workers to be present in person.
Residents should stay at home when not participating in essential activities like shopping for food, hardware supplies and medication. Gatherings should not be held beyond people inside a single home.
"The only time you should leave your home is for essential activities and needs," Mayor Eric Garcetti said.
The order takes effect Thursday at midnight for most and Friday at 11:59 p.m. for workers in businesses. It will last through April 19, possibly longer.
LA County public health director Barbara Ferrer said the order includes:
-- All public and private group events and gatherings of 10 or more people are prohibited anywhere in LA County. Smaller groups can gather if the organizer can guarantee social distancing of six feet and access to hand-washing or hand sanitizer.
-- Indoor malls, indoor shopping centers and nonessential retail businesses must close.
-- Indoor and outdoor playgrounds for children, except those at a child care center, must close.
These businesses and services will be allowed to continue. However, they must continue to practice social distancing and other protective measures.
-- Grocery stores, supermarkets, food banks, farmer markets, schools and child care centers.
-- Businesses and organizations that provide food, shelter, social services and other necessities of life for economically disadvantaged people.
-- Gas stations, banks and financial institutions and hardware stores.
-- Plumbers and electricians can continue to operate.
-- Media outlets can continue to operate.
-- Laundromats and dry cleaners can stay open.
-- Metro and transportation services and residential facilities can continue to operate.
The order is coming as the number of coronavirus cases in Los Angeles County continues to sharply increase. Earlier Thursday, health officials said Los Angeles County has 231 cases, including two deaths.
Gov. Gavin Newsom says state officials project that as much as 56% of the state's population - some 25.5 million Californians - could be infected over an eight-week period.
Related: Mayor Garcetti discusses $11 million initiative to help small businesses
Worldwide, the number of cases has exceeded 242,000 with more than 9,800 deaths, according to data from Johns Hopkins University. In the United States, the number of cases has risen to more than 13,000, with at least 175 deaths. California has seen 18 of those deaths.