The situation began around 5:30 a.m. when officers responded to a call of a man with a knife inside the restaurant on St. Charles Road and Route 83.
The man, 32, was working inside the closed restaurant as part of a third-party cleaning crew with two women, police said. The man was in a relationship with one of the women.
While they were cleaning, the man attacked his partner with two large knives inside the restaurant, according to police.
Both women escaped the building and asked a passerby to call 911.
One of the women was injured. The extent of her injuries was not disclosed.
Around 6:30 a.m., policed issued a community alert urging the public to stay away from the Elmhurst Crossing Shopping Center.
As the law enforcement presence grew, officers were unable to communicate or see where inside the restaurant the suspect was.
Chopper 7 was over the scene that showed SWAT teams at 8 a.m.
Man reportedly armed with knife in Portillo's restaurant, Elmhurst police say
At around 8:30 a.m. police entered the restaurant and found the man unresponsive with a self-inflicted injury, according to police.
The man was taken to a local hospital and is in custody of police while he receives medical care. The extent of his injuries is unknown.
A witness told ABC7 Chicago she saw a man come out of the Portillo's on a stretcher, but she didn't say much about his condition.
By 9 a.m., law enforcement surrounded the Portillo's with crime scene tape and began to leave the area.
The Portillo's will remain closed, as police process the crime scene inside the restaurant.
Elmhurst Crossing Shopping Center was cleared to open.
The DuPage County Metropolitan Emergency Response and Investigations Team assisted police with the situation.