PHILADELPHIA:Tension gripped the streets of Philadelphia for a second night on Tuesday following a deadly police shooting of a Black man armed with a knife and described by relatives as suffering from a mental breakdown as he was confronted by law enforcement.

A night after violent unrest and looting in the west Philadelphia neighborhood near where 27-year-old Walter Wallace was gunned down on Monday, hundreds of demonstrators marched again demanding racial justice while police and National Guard troops braced for more disorder.

As they had on Monday, Tuesday's rallies began peacefully but grew more confrontational as darkness fell, and police turned out in force to cordon off a section of the city's 52nd Street commercial district lined with shops that were looted the previous night.

Police in riot gear arriving in squad cars, on bicycles and on buses used their bikes to shove jeering protesters back from barricade lines. Aerial news footage broadcast by an NBC television affiliate also showed the looting of a Walmart retail outlet.

But Tuesday's clashes appeared for the most part smaller in scale and intensity than those on Monday, when orderly demonstrations gave way to violence that left 30 officers injured and led to more than 90 arrests.

Governor Tom Wolf, a Democrat, mobilized the Pennsylvania National Guard on Tuesday to assist law enforcement and city emergency management officials in maintaining order, a spokesman for the Guard said in a statement.

Monday's upheavals erupted hours after a bystander's video footage was posted on social media showing two officers opening fire on Wallace after he failed to heed their orders to back off and to drop the knife he was holding.

Wallace suffered from bipolar disorder, and his psychological difficulties were relayed by his wife to the officers who encountered him before the shooting, a lawyer for his family said.

The encounter transformed Philadelphia into the latest flashpoint in a months-long series of protests across the United States set off by the May 25 death of George Floyd, an unarmed African-American man in handcuffs, pinned by his neck to the street under the knee of a white Minneapolis policeman.

POLITICAL OVERTONES

The protests, and law enforcement response to them, have thrust the issues of racism and police conduct to the forefront of the White House race between Republican President Donald Trump and his Democratic Party challenger, Joe Biden.

"Our hearts are broken for the family of Walter Wallace Jr., and for all those suffering the emotional weight of learning about another Black life in America lost," Biden and his running mate, U.S. Senator Kamala Harris, said in a joint statement. "We cannot accept that in this country a mental health crisis ends in death."

Philadelphia and its predominantly minority population ranks as the largest city in Pennsylvania, a key battleground state in the Nov. 3 presidential election

Mayor Jim Kenney said the video of the Wallace shooting presented "difficult questions" about the actions of the officers involved.

"Last night we saw further evidence of the anguish of Black and Brown residents of our city who have struggled their entire lives under systemic racism," he told a news briefing.

But he also expressed sympathy for the officers injured in the protests, mostly from bricks and other projectiles hurled by demonstrators, and for the business owners whose shops were damaged.

"Vandalism and looting is not an acceptable form of First Amendment expression," Kenney said, referring to the constitutional right to free speech.

The video of Monday's shooting showed Wallace approaching two police officers who drew their guns after warning him to put down the knife. The video shows the officers backing up before the camera cuts briefly away as gunfire erupts and Wallace collapses.

Chief Inspector Frank Vanore said the police had responded to a call about a man screaming who was armed with a knife, and that each officer fired about seven rounds. But he declined to give further details pending the outcome of an investigation.

John McNesby, the president of the Fraternal Order of Police Lodge #5, defended the officers in a statement.

"The use of lethal force is a very difficult decision and we support our officers as they worked to resolve this incident under a great deal of stress. These officers were aggressively approached by a man wielding a knife," he said.

A relative of Wallace, Roosevelt Brant III, said the confrontation might have ended differently had police used a Taser stun gun to subdue his cousin.

"In this case, they had a gun, and that's what they use. They used deadly force," he told Reuters outside of the Church of the Christian Compassion in west Philadelphia, where Wallace's family, including his mother, gathered on Tuesday.