Investigators are looking into an apparent hazmat situation at Joint Base Myer-Henderson Hall in Ft. Myer, Virginia, after a number of people began feeling sick after opening a letter, officials said.

Arlington Fire, one of the units responding to the scene, said "11 people started feeling ill after the letter was opened" in an administration building. Three patients were hospitalized and were said to be in stable condition.

According to the U.S. Marines, personnel took “preventative measures” and evacuated people from the building.

“Several Marines are receiving medical care as a result of this incident,” they added.

According to a news release, the affected building was investigated and cleared.

"Joint Base Police Department officials are working with local HAZMAT teams, NCIS and the FBI," the news release said. "The letter was removed, and NCIS and FBI are conducting a joint investigation.

The letter was taken to a lab at Quantico for further examination, ABC News reported.

The base is located outside of Washington D.C., near the Pentagon.

Fox News’ Lucas Tomlinson and Jennifer Griffin contributed to this report.