Crime in some of the Bay Area’s largest cities fell sharply during the first week of the region’s shelter-in-place orders as streets emptied, shops shuttered and tens of thousands of people were forced to work from home.

The trend is a rare piece of good news amid the global coronavirus pandemic, and criminologists think it could hold as long as social restrictions remain in place.

Just after San Francisco ordered most businesses closed and barred nonessential gatherings and outings on March 17, the number of reported thefts, assaults and robberies in the city plummeted, according to The Chronicle’s review of recently released police data.

Violent crime was down 31% during the first week of the shelter-in-place order, compared with the same period in 2019. Property crime rates were nearly 50% lower during the same time frame.

In San Jose, violent crimes were down 45% and property crimes dropped 36% during the first week of the stay-at-home order, compared with the same period in 2019. The city had an especially big decline in robberies and residential burglaries, which plummeted by 56%, according to police data.

The total number of reported crimes in the South Bay city between March 15 and March 21 of this year was lower than any other week to date in the past two years, with a total of 373 incidents compared with an average of 548.

In Oakland, in the first week of the shutdown total reported crimes fell only slightly, tallying 250 incidents between March 16 and March 22, compared with 259 for approximately the same period in 2019. Violent crime rates were much lower, but property crime rates rose.

After an initial decline the week after social distancing was enforced, reported crimes started to climb back up in Oakland, fueled in large part by an uptick in burglaries and theft.

Despite fears that the health crisis could lead to lawlessness, declines in crime have been reported in cities across the country, from Philadelphia to New York to Los Angeles.

“Commercial crime depends largely on opportunity,” and with so many people at home, those opportunities are mostly gone, said Richard McCleary, a professor of criminology at UC Irvine. “I think this will be normal as long as everyone is staying inside.”

While street crimes have dropped, experts fear that problems that typically occur inside the home — such as child abuse, battery and domestic violence — could increase as people remain stuck in close quarters amid stressful conditions. And without adequate measures to address the economic fallout caused by the coronavirus, some criminologists cautioned that the pandemic could fuel an uptick in certain crimes, particularly at empty businesses.

“The only thing that scares me a little is when the deprivation starts to hit,” said James Lynch, a professor at the Department of Criminology and Criminal Justice at the University of Maryland. “Some people are going to be left out, they’re going to be in pretty desperate shape, and you can see them trying to do something for money.”

The FBI has also warned about an increase in hate crimes against Asian Americans, according to ABC News, and there’s concern about a rise in cybercrimes and online scams.

San Francisco police officers plucked from narcotics units and other investigative units were reassigned to street patrols during the first few weeks of the shelter-in-place orders, bracing for an influx in crimes of opportunity.

But officers recently walking the beat near Sixth and Market streets reported mostly business as usual, if not a slow shift. The most action Officers Samuel Fung and James Puccinelli saw by Thursday afternoon were unlicensed street vendors and an overdose at Golden Gate Avenue and Market Street.

“People walking around and that’s about it,” Puccinelli said, motioning toward a few lone stragglers on Sixth Street. “It’s been a quiet day.”

Officer Robert Rueca, a San Francisco police spokesman, said the department has noticed less traffic on the streets, both vehicle and pedestrian.

“We are seeing fewer incidents,” he said. “There are fewer people out, and that equates to fewer people being likely to be victims in any kind of criminal activity.”

Rueca speculated that residential burglaries have fallen because more people are staying home. Uniformed officers have also expanded their presence in commercial areas, where rows of empty storefronts are especially vulnerable to smash-and-grabs. Some storefronts have been boarded up to deter looters.

“There isn’t one particular business corridor we are not looking out for,” Rueca said. “Employees like to feel like we are watching these businesses.”

Law enforcement officials said it’s still too early to draw solid conclusions from the short-term decline in crime, but it appears to be driven by the dearth of social interaction.

Almost all types of crime in San Francisco — assault, burglary, larceny, robbery and car theft — fell during the first week of the shelter-in-place order, according to San Francisco police data, and every part of the city saw a notable decline in reported incidents compared with the same period last year.

District Attorney Chesa Boudin said many crimes in San Francisco target visitors to the city — a population that has mostly vanished.

“A significant percentage of auto burglaries and robberies were being committed against tourists and people visiting San Francisco, and sadly we don’t have that tourism right now, but it also has resulted in a significant decrease in crime rates,” Boudin said. “Our challenge will be after the crisis is over, to keep the crime rates down.”

Joaquin Palomino and Megan Cassidy are San Francisco Chronicle staff writers. Email: jpalomino@sfchronicle.com, megan.cassidy@sfchronicle.com Twitter: @joaquinpalomino, @meganrcassidy