PHILADELPHIA — A tense Philadelphia braced for more demonstrations Wednesday over the police killing of a Black man following two nights of protests that set off clashes with police and break-ins of stores on the other side of the city.

The death of Walter Wallace Jr., who was fatally shot by police Monday after authorities say he ignored orders to drop a knife, came amid already-heightened tensions in the battleground state just days before the election.

About 500 people gathered in a West Philadelphia park Tuesday evening, marching to the nearby police headquarters where officers were stationed with riot shields. Some of the demonstrators threw debris at officers, according to police, and both sides later clashed.

Police said two officers were injured, although authorities did not disclose the extent of their injuries.

Some business owners were cleaning up damage and boarding up windows and doors Wednesday after video showed people streaming into stores and stealing goods on the opposite side of the city from where Wallace was shot. The National Guard is slated to arrive in the next few days to focus on guarding infrastructure, state and city officials said.

The clashes come as Pennsylvania emerges as a key focus of the contentious 2020 election, with President Donald Trump and former Vice President Joe Biden, a native son, locked in a battle for the state’s 20 electoral votes. Both candidates have made frequent campaign stops in the state.

More than 9 million Pennsylvanians have registered to vote, and many in Philadelphia waited in line for hours this week to request a mail-in ballot by Tuesday’s deadline, as news of the police shooting spread.

Mayor Jim Kenney, a Democrat, said Tuesday the city had been through “a very difficult time” but said vandalism was not the answer.

“There were a lot of peaceful protesters out there last night,” Kenney said at a news conference on Wallace’s death. However, he said violence “is not an acceptable form of First Amendment expression.”

A Kenney spokesperson said Wednesday the city has requested help from the Pennsylvania National Guard to help with “the current situation and election preparation.” Specific details were still being worked out, and none have yet been deployed.

The unrest started Monday evening, shortly after Wallace, 27, was killed and set off protests elsewhere, including in Washington, D.C., the Brooklyn borough of New York City and Portland, Oregon, where demonstrators held their hands in the shape of a “W” in his honor.

Police said Wallace was wielding a knife and ignored orders to drop the weapon before officers fired shots Monday afternoon. But his family’s lawyer said the family had called for an ambulance to get him help with a mental health crisis. His parents said Tuesday that officers knew their son was in a mental health crisis because they had been to the family’s house three times Monday.

Wallace’s wife, Dominique, is pregnant and was scheduled to be induced Wednesday, according to the family’s attorney, Shaka Johnson. Johnson said Wallace had nine children, two of whom briefly spoke at a news conference late Tuesday, along with Wallace’s mother and father.

“When you come to a scene where somebody is in a mental crisis, and the only tool you have to deal with it is a gun ... where are the proper tools for the job?” Johnson said, arguing that Philadelphia police officers are not properly trained to handle mental health crises. Johnson said Wallace’s brother had called 911 to request medical assistance and an ambulance.