According to media reports, the gunman was killed during a gunfight with the police.

Aurora is located 40 miles west of Chicago city.

The first 911 calls came to Aurora police around 1:24 p.m. CT, with callers saying there was an active shooter at the Henry Pratt Company, which says it is one of the United States' largest manufacturers of industrial valves, as per CNN report.

An employee at the company, John Probst, told CNN affiliate WLS the shooter was a co-worker and had a pistol.

Aurora Chief of Police Kristen Ziman was quoted as saying by CNN that the shooter was killed by the officer.

Police have identified the shooter as Ziman as Gary Martin, 45.

Police said the motive behind the attack is still not known.

The injured people were rushed to hospital for treatment, media reports said.

US President Donald Trump reacted to the incident and posted: "Great job by law enforcement in Aurora, Illinois. Heartfelt condolences to all of the victims and their families. America is with you!" 

U.S. Senator from Illinois Tammy Duckworth condoled the loss of lives in the tragedy.

"My heart hurts for the victims, their families, the brave first responders, Aurora and all of Illinois right now. Our nation’s epidemic of deadly gun violence is a real national emergency," Tammy tweeted.

Police in Aurora, Colorado earlier posted that the shooting incident was not taking place in Colorado.

Aurora Police Department tweeted: "THE #ACTIVESHOOTER IS IN AURORA ILLINOIS, NOT IN OUR AURORA COLORADO. We hope everyone will be okay, and the situation is resolved quickly for all involved. Please follow @AuroraPoliceIL for information on that incident."

In Colorado, a man had opened fire in a cinema theatre in 2012.