Authorities were on the scene at Columbia Mall, and three people have been confirmed dead, Howard County chief of police Bill McMahon said in a press conference.
"We are very confident it was a single shooter," McMahon added, noting that authorities did not believe there were any more shooters in or around the mall.
"This shouldn't happen in Columbia Mall. It shouldn't happen anywhere," McMahon said.
The Howard County Police Department provided a series of updates on its Twitter feed and indicated that police were alerted at 11:15 a.m. that shots were fired.
McMahon told reporters that the three victims were found in a Zumiez skateboard store on the upper level of the mall overlooking the food court, and one was found near a shotgun and ammunition.
"One of those victims appears to be the shooter," McMahon said. He added that the gunman apparently shot two people and then shot himself.
While the gunman has not yet been named, the victims have been identified as Brianna Benlolo, 21, of College Park, Md., and Tyler Johnson, 25, of Ellicott City, Md. Both were employees at the Zumiez store.
ABC News reports that the shooting was a possible domestic dispute involving a husband, his estranged wife and her boyfriend, but police said they could not confirm a motive at this time.
The gunman was found with "a large amount of ammunition still on and about him," McMahon said, and experts were brought in to make sure that he didn't have any explosive devices on or near his body.
McMahon described the incident as "a chaotic scene ... It's a crowded mall – you know how many people are in there on a Saturday afternoon."
He added that "many, many people" secured themselves in stores, and noted that detectives were questioning eyewitnesses as they exited the mall, which has now been cleared.
Five people were treated at Howard County General Hospital, including one person who suffered a gunshot wound to the foot.
Jose Luis Magana / AP