Employees of WMAR-TV left by a back door to the building in Towson, Md., but police said some might still be hiding inside. Police said the man in the building could have weapons.
The incident began about 11:45 a.m. Allison Bourg, a digital reporter, told the Baltimore Sun she heard banging on the front door.
The security guards told her to get out of the area, and the news director then began shepherding the staff out of the building, Bourg said.
"A guy has slammed his truck 7 times into our building and is in our building ... we've been evacuated," Mike Masco, the WMAR meteorologist, said via Twitter.
When police arrived they found the truck in the lobby with no one inside.
Most of the staff remained in the parking lot. St. Pius Roman Catholic Church and its parochial school, both near the station, were under lockdown, and police warned area residents to stay away from the neighborhood.
WMAR is the ABC affiliate in Boston. The office and studios are in Towson near the Baltimore line.