GUNMEN have opened fire on picnics in Detroit and Philadelphia, killing one and injuring 16, including an 18-month-old baby.

Philadelphia Police Lieutenant John Walker told NBC affiliate WCAU that a gunman shot down a street where people were gathered for a party on Saturday.

“It appears that everybody was here for the picnic and everybody just ran ... it looks like they just randomly fired down the street and just hit whoever was in their way,” Mr Walker said.

“It looks like they just randomly fired down the street and hit anyone in their way.”

He said the incident was “just a terrible situation”.

The news station said one of the victims was an 18-month-old baby who was grazed with a bullet in the neck. The other was a 10-year-old boy.

The other five victims, aged 15 to 25, were taken to hospitals after the shooting, which occurred around 10pm as the car turned a corner.

Meanwhile, in a similar incident in Detroit on Saturday, one person was killed and nine others injured when a suspect opened fire at a party on a basketball court during a children’s party.

“It’s a miracle that not one kid is shot,” Assistant Police Chief Steve Dolunt told Fox2.

“I don’t know what the hell these people were thinking with this many kids out here. I’m livid. There’s no excuse for this,” Dolunt said.

Dolunt said a 20-year-old man was killed. He was not being identified while relatives were informed.

Another man was critically injured and eight others, five men and three women, were listed as seriously injured. The victims ranged in age from 21 to 46, he said.

The shooting happened at a neighbourhood party that included a barbecue attended by families with some small children in strollers.

Dolunt said police do not yet know the reason for the shooting.

About 400 people were at the party when the shooting happened, Click On Detroit reported.

#BREAKING DPD comb bball court after 5 people shot at Webb & Dexter. 1 dead, 1 critical. 3 others injured #local4 pic.twitter.com/rduSG0lFxC — Priya Mann (@Local4Priya) June 21, 2015

The shootings come after nine African Americans were killed in a church in Charleston, South Carolina, by a suspected white supremacist.

The massacre has reignited a debate about gun laws in the United States.