He urged the community to avoid the area and advised that a re-unification center had been set up at a nearby mall.
A spokeswoman for a hospital near the newspaper said two patients had arrived there but she did not know their conditions.
Capital Gazette reporter on CNN: "I'm going to need more than a couple days of news coverage and some thoughts and prayers, because it's our whole lives have been shattered".
One of the group's flagship papers, the Capital, plans to publish a Friday edition, several reporters with the group said. That location is a commercial development in which The Capital Gazette is a tenant.
As he waited to be interviewed by the police, Phil Davis shared information with the public on Twitter.
Davis said a single shooter shot through the glass door to the office and opened fire, hitting several of his colleagues.
Police - who said they reported to the scene of the crime within a minute and a half - evacuated the premises, ushering people out of the building with their hands up, and continued to search the building. Members of Anne Arundel County law enforcement subsequently told reporters that a long gun had been used in the shooting and that investigators recovered what appeared to be an explosive device from the scene.
Amazon to Acquire PillPack
Neil Saunders of the research firm GlobalData Retail, said the Amazon acquisition "is a warning shot" for the pharmacy sector. Terms of the deal were not disclosed, but TechCrunch reported the deal was for "just under $1 billion".
Anne Arundel County Acting Police Chief William Krampf confirmed the deaths Thursday at a news conference.
The shooting - which came amid months of verbal and online attacks on the "fake news media" from politicians and others from President Donald Trump on down- prompted New York City police to immediately tighten security at news organizations in the nation's media capital.
In a later interview, Davis said it "was like a war zone" inside and said it was a situation that would be "hard to describe for a while".
"Can't say much more and don't want to declare anyone dead", he wrote. Frashure said officers are still clearing the building and must look for other dangers, such as bombs and other shooters. "I don't know why he stopped", he said. He says police are first trying to make sure everyone in the building gets out safely and that there are no bombs inside.
The Capital-Gazette is a subsidiary of the Baltimore Sun, one of the Tronc's newspapers. "Thank you to all of the First Responders who are now on the scene".
The Governor of Maryland, Larry Hogan, wrote on Twitter he was "devastated" upon hearing about the incident.
The ATF in Baltimore confirmed it was responding to the scene.
He says, "My thoughts and prayers are with the victims and their families" and thanks "all of the First Responders who are now on the scene".