Philadelphia’s gun violence epidemic reached alarming heights Sunday, as 23 people were shot across the city — the most in a single day since at least 2013. Six of the victims died, including a 6-year-old boy who police believe was mistakenly shot by a 5-year-old boy inside an Upper Holmesburg rowhouse.

The violent surge capped a July 4th holiday weekend in which 35 people were shot between Friday morning and Sunday night, according to police. The victims included an 11-year-old girl grazed by a bullet in Elmwood, a 52-year-old man shot in the foot while riding a bike in North Philadelphia, and a 15-year-old boy who died after being shot in the head during a triple shooting in Overbrook.

Police said most of the cases had not yet resulted in arrests. On the block where the 6-year-old was killed, neighbors said they were shocked to learn a child died inside with other kids nearby.

So far this year, at least 888 people have been shot in the city, according to an Inquirer analysis of city and police data — an average of 4.7 people per day. The number of shooting victims has been steadily increasing since 2014, when 1,047 people were shot.

If this year’s pace holds, the city will reach that number by early August — and will finish the year with more than 1,700 victims, the highest total since at least 2007.

Homicides, which also have been steadily rising in recent years, have continued to surge in 2020. According to police statistics, 210 people have been killed in the city this year, 27% above last year’s total through the same date, putting the city on pace for its highest annual murder tally since 1997.

Mayor Jim Kenney on Monday lamented the violence, saying police resources have been stretched thin by the ongoing protests sparked by the police killing of George Floyd in Minneapolis. He added that violent situations can sometimes result from people being stuck in their homes for a long time because of the coronavirus pandemic.

City Council President Darrell L. Clarke said the city was facing a “perfect storm” of problems, including widespread poverty, the coronavirus, the ongoing unrest, and easy access to guns — issues he said Council was working to improve.

“At the end of the day, we’ve got to get through this,” Clarke said. “We got to figure out a way.”

Police Commissioner Danielle Outlaw was not available for an interview, the department said.

The steady uptick in gun violence this year began with an especially brutal January and continued even after the emergence of the coronavirus, when shootings and homicides continued unabated as other violent crime generally decreased during the city’s stay-at-home order.

Other cities across the country — including Chicago and New York — have also seen spikes in gun violence in recent weeks, even as overall reported crimes have fallen.

Jerry Ratcliffe, a criminal justice professor at Temple University, said Monday that determining causes for the spikes could be a challenge. In Philadelphia, so much has changed during the pandemic and subsequent social unrest: More people are staying home, more people are unemployed, police have shifted arrest and enforcement tactics to protect public health, and a broad public conversation has been taking place about the use of force by police.

“You’ve got multiple things taking place at once, and it’s hard to disentangle the effects of each one,” he said. “Some of these factors will compound each other, some may dissipate, but we just don’t know.”

Thomas Abt, a senior fellow at the Council on Criminal Justice, cautioned in a report he coauthored and released last month that killings could rise during the rest of 2020 for several reasons, including cuts in city services, difficulty in safely conducting anti-violence outreach during a public health crisis, and worsening police-community relations amid the unrest over Floyd’s death.

“We have a lot of things going on at the same time, and unfortunately most, if not all, of these factors are pushing crime and violence in the wrong direction,” Abt said in an interview.

Meanwhile, Bilal Qayyum, a longtime anti-violence advocate in Philadelphia, said the lack of jobs and opportunity in many communities of color had only intensified as the pandemic exposed long-standing inequalities.

“That kind of pressure consistently on a community, without any signs of changing, I really believe is helping drive the violence we’re seeing right now,” he said.

In addition to systemic issues, Kenney has said police faced unprecedented deployment challenges during the first several days of the protests. Police statistics show 35 people were shot during the first two days of the demonstrations, on May 31 and June 1, though the majority did not occur in areas where protests took place.

Beyond simply recording more victims this year, the frequency of shootings has been on the rise. According to an Inquirer analysis of city data, only 3% of this year’s 186 days have passed without a shooting — the smallest percentage of any year since 2013.

Meanwhile, 45% of this year’s days have ended with at least 5 people shot. And at least 78 of this year’s victims have been age 17 or younger, with 10 of this year’s victims getting shot before they reached age 13.

One of them was Fakeem Hayes, the 6-year-old boy killed about 1 p.m. Sunday inside a house on the 4600 block of Kendrick Street.

Staff Inspector Sekou Kinebrew, a police spokesperson, said investigators believe a 5-year-old boy inside the house shot Fakeem by accident. The child did not live at the house where he was shot, said Kinebrew, who added that detectives were “still trying to sort everything out, and our best witnesses are young children.”

Outlaw told reporters at the scene Sunday that an adult was home with the children when the shooting occurred, and that a neighbor “transported that adult and the young boy to the hospital.”

No one answered the door Monday at the two-story redbrick rowhouse where the shooting happened. A small blue inflatable pool sat on the front lawn, and two red-and-blue kids’ bikes were parked on the concrete walkway in front of the house.

Neighbors said the people who live in the home kept to themselves. Biolanny Gil, 29, said: “There are so many people coming in and out of the house. You don’t know who actually lives there.”

Other neighbors said they believed there was drug activity at the house and another on the block. A woman who asked to remain anonymous for fear of retribution called the houses “problem homes for a very long time.” She said she did not know who lived there.

The woman said she initially believed that police visiting the house Sunday afternoon had done so as part of a drug bust. She was saddened to learn it was instead for the death of a young boy.

“The whole neighborhood was shocked to hear that had happened,” she said.

People gathered outside the West Oak Lane house where police said Fakeem lived declined to comment Monday.

Meanwhile, unrelated shootings continued in the afternoon.

Just before 2 p.m., a 22-year-old woman was shot in the foot in East Germantown, police said.

Two hours later, on the 4600 block of Broad Street in Logan, a 41-year-old man was pronounced dead at the scene after being shot in the head and neck.

Staff writers Sean Collins Walsh and Hadriana Lowenkron contributed to this article.