Several victims including a police officer injured as an active shooter opened fire inside a Chicago hospital

                         
An unknown number of people have been wounded, including a police officer, after an 'active shooter' attack at a Chicago hospital.

According to reports, the Chicago police officer was critically injured after gunfire broke out at Mercy Hospital, located in the city's South Side, around 3.20pm on Monday. Police spokesman Anthony Guglielmi said the officer is 'in critical condition but receiving excellent care' at University of Chicago Hospital.

The gunman reportedly targeted a woman who was dressed in hospital scrubs in Mercy's parking lot and shot her multiple times. An official said that fewer than six people were believed to have been shot and at least 'one possible offender' was also shot.

An eye witness identified as Hector Aditia said he saw the gunman shoot one victim 'multiple times in the parking lot' and then exchange gunfire with responding officers. A fellow witness Maria Correa told CBS Chicago she heard multiple shots and saw blood in one of the hospital's entrances.

Police are continuing to do a 'methodical search' of the hospital, according to Guglielmi while emergency crews were called to the hospital around 3.20pm and 15 ambulances arrived at the scene.