SAN FRANCISCO — The mayor of San Francisco on Friday declared a state of emergency in one of the most crime-ridden and drug infested parts of the city.

That area, the Tenderloin neighborhood, is just steps from city hall, but it has been ground zero for drug dealing, overdose deaths and homelessness for years.

In what many observers said was a sharp turnaround in both tone and policy, the mayor, London Breed, this week said she would pursue an “aggressive” crackdown on the “nasty streets” of her city. It’s a highly unusual move by a liberal mayor in one of the country’s most liberal cities.

“We are in a crisis and we need to respond accordingly,” she said at a news conference on Friday. “Too many people are dying in this city, too many people are sprawled on our streets,” she said, referring to residents who have overdosed.

Twice as many people died of drug overdoses in San Francisco last year than died from the coronavirus.

Earlier this week, Ms. Breed acknowledged that many of her progressive constituents would push back on her efforts, but she said, “We can’t do the same thing every day and expect different results.” She said she recognized that San Francisco was a compassionate city, but “we’re not a city where anything goes.”

The announcement is part of a series of initiatives intended to disrupt street sales of stolen goods, expand police surveillance powers and give people who use drugs in the open a choice between treatment or jail. She said that declaring a state of emergency would allow the city to cut through red tape and increase funding to the police, who she said had already arrested 23 people during felony warrant sweeps.

The Declaration of Emergency must be ratified by the city’s Board of Supervisors within the next seven days, and would remain in effect for no longer than 90 days.

Crime statistics provided by the San Francisco Police Department show that several categories of crime are down over 2019, the last year before the pandemic. So far this year, there have been almost 29,000 reports of larceny, an increase over last year but well below the nearly 40,000 larcenies reported in the same period of 2019. Homicides have increased to 53 so far this year from 37 in 2019.

Burglaries were up sharply in 2020 but have declined slightly this year, and motor vehicle thefts also spiked in 2020 and have stayed about the same this year.