A reporter for the Capital Gazette, Phil Davis, tweeted that a "gunman shot through the glass door to the office and opened fire on multiple employees." He said several people were killed.
"There is nothing more terrifying than hearing multiple people get shot while you're under your desk and then hear the gunman reload," Davis said.
Up to four people had been killed, according to CBS News quoting two sources.
The newspaper is located in a four-story office building in Annapolis, the capital of the US state of Maryland.
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The White House said President Donald Trump had been briefed.
"ATF Baltimore is responding to a shooting incident at the Capital Gazette in Annapolis," the Bureau of Alcohol, Firearms, and Tobacco said on Twitter.
The local Anne Arundel police force added: "Confirming active shooter at 888 Bestgate Road in Annapolis. Building evacuated. Officers continuing to search building."
"Absolutely devastated to learn of this tragedy in Annapolis," Maryland Governor Larry Hogan said. "Please, heed all warnings and stay away from the area. Praying for those at the scene and for our community."