Twelve people including a three-year old toddler have been injured after a gunman opened fire in a park on Chicago's South Side.

Authorities said two of the victims, as well as the toddler, are in critical condition.

The alleged shooting rampage took place late in the evening. Ten ambulances were sighted near the crime scene.

Dozens of police officers swooped on next to a basketball court in the park.

A 22-year-old witness, Julian Harris, told Chicago Sun Times that the suspects were dreadlocked young men carrying weapons and claimed there was a gang link.

"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," said Harris.

Chicago Police said they could only confirm that multiple shots were fired. No one had been taken into custody, they said.

Chicago has been experiencing a sharp increase in gun violence recently. According to latest FBI report, Chicago had 500 homicides in 2011 compared to 431 in the previous year.

The incident comes just days after Aaron Alexis went on a shooting spree at Washington Navy Yard, killing 12 people.