Mass shootings broke out at festivals, block parties and other gatherings in a handful of cities this week as the US marked Independence Day.

Gun violence that flared in Washington, DC, Louisiana, Florida, Philadelphia, Texas and Baltimore left more than a dozen dead and almost 60 wounded — including children as young as two years old.

In Shreveport, Louisiana, at least three people were killed and 10 others wounded late on Tuesday night, Shreveport police Sergeant Angie Willhite said. One of the injured was in critical condition on Wednesday but the others were expected to survive, she said.

No arrests have been made.

“We are struggling with getting information from those who were present. We’re not getting a lot of cooperation,” Willhite said.

The discovery of another body found in the area on Wednesday morning was likely to be connected, police Chief Wayne Smith said at a news conference.

The block party where the shooting took place has been held around the July Fourth holiday for at least 10 years, said Shreveport City Councilwoman Tabatha Taylor, who represents the neighbourhood.

Independence Day celebrations in the nation’s capital also turned violent when nine people outside enjoying the festivities were shot and wounded early in the day, police said.

Officers who responded about 1am local time to the mass shooting in a neighbourhood about a 20-minute drive east of the White House found a nine-year-old and a 17-year-old among the victims, Metropolitan Police Department Assistant Chief Leslie Parsons said.

The victims, who were not publicly identified, were hospitalised with injuries that weren’t considered life-threatening, police said.

The gunshots were fired from a dark SUV seen driving through the neighbourhood, Parsons said, calling the shooting targeted. It was unclear if there was more than one shooter in the vehicle, and no arrests had been made, police said.

In Florida, gunfire erupted after an altercation between two groups gathered for July Fourth celebrations along a causeway that crosses Tampa Bay, killing a seven-year-old, police said.

Investigators said the boy was sitting in a truck with his grandfather on Tuesday when a bullet was fired into the vehicle, hitting the older man in his hand and the boy in the head.

Calvin Johnson, deputy chief of the Tampa Police Department, said no arrests had been made but investigators don’t believe the boy and grandfather were targeted.

The shooting stemmed from an argument over jet skis that one group said were coming too close to children playing in the water.

“There was no reason — no excuse that an argument can lead to gunfire, much less an argument over jet skis,” Johnson said at a news conference.

“Now we got citizens’ families, folks in our communities, that have to deal with this tragic incident that happened on Fourth of July.”

Even before the holiday, city streets turned deadly in other communities.

On Monday night, a shooter in a bulletproof vest opened fire on the streets of Philadelphia, killing five people and wounding two boys, ages two and 13, before surrendering, police said.

Three people were killed and eight others were injured when several men fired indiscriminately into a crowd of hundreds that had gathered in a Texas neighbourhood after a festival in the area, authorities said. The shooting in the Fort Worth neighbourhood of Como happened late Monday night, about two hours after the annual ComoFest ended.

Thirty people were shot, two fatally, at a block party in Baltimore early Sunday. Many of those shooting victims were children, authorities said.

-AAP