Senior law enforcement officials confirmed with CBS News that the suspect is a white man in his 20s and didn't have identification on him.
Marc Limansky, a spokesman for the Anne Arundel County Police Department, said officers were searching the building while trying to get everyone out safely.
"This was a targeted attack on the Capital Gazette", Krampf said.
The newspaper's website lists 20 newsroom employees.
A law enforcement official speaking on the condition of anonymity told The Associated Press that the suspect mutilated his fingers in an apparent attempt to make obscure his identity. Smoke bombs and flash bang devices were found in his backpack, a source said. Police would not confirm whether they were shot inside the newspaper's newsroom.
Davis also said that he could hear the shooter reload their weapon. They were brought to a re-unification center that had been set up at a nearby mall.
Following first reports of a shooting around 2:40 p.m., police cars were seen swarming the scene while people were seen streaming out of the building with their hands up. "We'll have more information for you in the next briefing", acting police chief of Anne Arundel county Bill Krampf told reporters.More news: There are no accidents in Melania Trump’s wardrobe choices
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The suspect, described as a white male who was believed to have used a shotgun, was in custody. "I can tell you this: We are putting out a damn paper tomorrow", reporter Chase Cook wrote on Twitter a few hours after the shooting. We are monitoring the horrific shooting at the Capital Gazette in Annapolis.
Maryland governor Larry Hogan said on Twitter he was "absolutely devastated" and was in contact with authorities.
He and Schuh praised local law enforcement for their quick response, which they said prevented further bloodshed. Up to four people had been killed, according to CBS News quoting two sources. One patient was being treated at the University of Maryland Medical Center, a spokesperson confirmed.
Several people with serious injuries were sent to University of Maryland Shock Trauma Center in Baltimore. The shooting took place right before noon on Thursday.
The Capital Gazette is a newspaper owned by The Baltimore Sun.
Police went to the offices of the Baltimore Sun as a precaution, the Gazette reported.
The MailOnline reported that Phil Davis, who identified himself as a "courts and crime reporter" at the Capital Gazette, tweeted that multiple people had been shot.