He said he did not know the relationship between the gunman—described as a man in his 30s—and the doctor. The hospital said in a statement that the doctor is a faculty physician but that it could not release more information because of privacy policies.
A small area of the hospital remained locked down and police were preparing a tactical operation to deal with the gunman, Guglielmi said. However, he said the gunman had not taken any hostages, and people with appointments in other parts of the hospital were encouraged to keep them.
"We're good at these kind of things, and we're confident that we're going to get this situation resolved very soon," Guglielmi said.
The FBI was assisting Baltimore police, said FBI spokesman Richard J. Wolf.
Hopkins spokesman Gary Stephenson said the affected area was the eighth floor of the Nelson building, the main hospital tower. Guglielmi said the situation was contained to that part of the hospital, and no people were locked in rooms or otherwise in danger.
According to the Hopkins website, the eighth floor is home to orthopedic, spine, trauma and thoracic services.
About a dozen officers wearing vests and helmets and carrying assault weapons prepared to enter the hospital at midday.
The rest of the massive hospital, research and medical education complex remained open, including the emergency department.
With more than 30,000 employees, Johns Hopkins Medicine is among Maryland's largest private employers and the largest in Baltimore. The hospital has more than 1,000 beds and more than 1,700 full-time doctors.
Modern Healthcare reported earlier this month that two visitors to Baton Rouge (La.) General Medical Center's Mid City hospital were injured after shots were fired inside the hospital. The shootings stemmed from “a purported domestic dispute” that led to a four-hour lockdown of the hospital, officials there said.
In April, a gunman killed himself and a patient and injured two other people outside of the Parkwest Medical Center in Knoxville. The three women victims, who were shot outside the patient discharge area, were current or former employees of the hospital. Police would not speculate on the gunman's motives.
The Joint Commission issued a sentinel event alert in June warning that an increasing number of violent crimes like assaults, murders and rapes were taking place at healthcare facilities. The commission advised hospitals to take extra security measures in their emergency departments and to reassess their violence-prevention programs.
“Unfortunately, healthcare settings are not immune from the types of violence that are found in the other areas of our lives,” Joint Commission President Mark Chassin said in a June statement.