13 people including a 3-year-old boy were injured in a Chicago park last night in what police believe was a gang-related shooting.

It is thought the incident happened in the Back of the Yards neighbourhood on the city's South Side at 10.15pm local time on Thursday night.

A 3-year-old boy was wounded in the cheek while 4 of the other victims are also in critical condition, officials said. 

"We had multiple victims shot, who were transported to various hospitals throughout the city," said James Mungovan, Deputy District Chief of the Chicago fire department.

Witness Julian Harris, the 3-year-old boy's uncle, told the Chicago Sun-Times men fired at him from a grey sedan before turning towards Cornell Square Park and firing at people in the area.

"They hit the light pole next to me, but I ducked down and ran into the house.

"They've been coming round here looking for people to shoot every night, just gang-banging stuff. It's what they do."

Francis John, 70, said she was in her apartment when the shooting occurred.

She said went down to see what was going on and "a lot of youngsters were running scared".

She was surprised by what had happened, saying she has lived in the area for 30 years.

No one is believed to be in custody.

FBI figures have shown that Chicago has overtaken New York to become the murder capital of the US with 500 deaths in the last year.

President Barack Obama returned to his adopted hometown earlier this year to appeal for an end to the "senseless" gun violence ravaging Chicago.

He pressed for ambitious gun control measures, which so far have been stalled in the US Congress.

Chicago Tribune overnight reporter @peternickeas uploaded videos from the scene to Instagram a short time ago: