Chicago, IL – Four people were taken to the hospital after a carbon monoxide incident Monday evening on Chicago’s West Side, fire officials confirmed.

The incident was reported before 5:45 p.m. in the 2000 block of West Fulton Street. Two people were taken to Stroger Hospital in serious-to-critical condition, while a third victim went to the University of Illinois Hospital in fair-to-serious condition.

Information about the fourth victim was not immediately known. Carbon monoxide levels were elevated by the use of a portable motor, officials said.

The building was evacuated as a result of the incident. Firefighters were using fans to lower the carbon monoxide levels on Monday evening.