US mass shooting leaves 2 dead, half of 28 injured were children

A mass shooting early on Sunday at an outdoor neighbourhood block party in Baltimore, Maryland, left two people dead and 28 others injured, about half of them children, as investigators sought the public's help in tracking down multiple suspects, police said.

Authorities offered no motive for the gun violence, which erupted at about 12.35am local time in a courtyard of grass and pavement between a pair of two-story rowhouse structures in South Baltimore's Brooklyn Homes community.

The two people slain in the hail of gunfire were identified by police only as an 18-year-old woman and a 20-year-old man. As of Sunday afternoon, nine others wounded remained hospitalised, a few of them listed in critical condition, police told reporters.

Among the 28 survivors who were injured were an estimated 14 who were under the age of 18, said Richard Worley, acting commissioner of the Baltimore Police Department, noting that they were still trying to confirm victims' ages.

Baltimore television station WBAL-TV, an NBC affiliate, reported that ages of those who were injured ranged from 13 to 32.

The shooting likely ranks as Baltimore's largest single act of gun violence in terms of number of victims dating back to 2014, according to the Baltimore Sun newspaper, citing the earliest data kept by the nonprofit Gun Violence Archive.

The extent of the carnage was notable even for a city that has long grappled with high levels of homicide and other violent crimes.

Worley said police were searching for multiple suspects, and he appealed to the community to come forward with any information or videos that might help investigators identify the perpetrators.

"We know for sure there are more than one. We don't know how many (suspects)," Worley said.

One resident of the neighbourhood, Terry Brown, told the Baltimore Sun said he was standing outside his home when he heard the crackle of gunfire, followed by a stampede of people fleeing in panic for cover.

"It was chaos," Brown said. "Parents were running around looking for their children, hollering and screaming, and don't know if their child has a bullet in them."

Mayor Brandon Scott called the shooting a reckless, cowardly act," and vowed that those responsible would be brought to justice. "We will not stop until we find you, and we will find you."

The tragedy rattled the city of Baltimore, Maryland's most populous city, 64km northeast of Washington DC, at the start of the Fourth of July holiday weekend, at a time when Americans typically gather for parades, barbecues and fireworks.

Local media reported that hundreds had attended the "Brooklyn Day" block party, which featured pony rides, dancing and refreshments.

One witness interviewed by television station Fox 45 recounted hearing 20 to 30 gunshots.

Television footage of the crime scene on Sunday showed police tape blocking off a grassy area littered with overturned tables, cups, plates, and other trash from the event.