Four killed in another US mass shooting

At least four people were killed and two children wounded in a mass shooting Monday night in the US city of Philadelphia, police said, the latest chapter in the country's gun violence crisis.

Those killed were all males aged between 20 and 59, Philadelphia police commissioner Danielle Outlaw told journalists, while the two children wounded were aged two and 13.

Police apprehended the suspected shooter -- a 40-year-old who was wearing a bulletproof vest and was armed with a rifle and a handgun -- near the scene of the shooting in the city's Kingsessing neighbourhood, Outlaw said.

"I don't know if he was firing the rifle at the time we were pursuing or the handgun, but yes he was actively shooting a firearm at the time our officers were pursuing," she said.

Earlier local media reports said four people had been hurt in the shooting, but Outlaw put the number of wounded at two, both children.

Local media footage showed police had cordoned off an extensive crime scene, which Outlaw said spanned at least eight city blocks. 

"We have absolutely no idea why this happened. Like I said we have this person in custody and we are doing what we can to positively identify this person," she said.

Police said they had also apprehended a second person, who they believe returned fire against the shooter.

"At some point as victims were being shot, we have another person that we believe acquired a gun somehow... and returned fire in the direction of the shooter that we have in custody," said Outlaw.

Monday's shooting was at least the 341st that the United States has seen this year, according to the Gun Violence Archive (GVA), with at least 21,696 people killed -- including 12,144 suicides -- so far this year.

The GVA defines a "mass shooting" as a gun-related incident in which at least four or more people are wounded or killed. 

Last year, at least 44,357 people were killed in gun violence in the United States, more than half of which were suicides. 

Over the weekend, two people were killed and 28 wounded in a shooting at a block party in the eastern city of Baltimore.