Homeland security chief says unfolding situation at Andrews

Homeland Security Secretary Jeh Johnson says there is an "unfolding situation" at Joint Base Andrews in Maryland but is providing no further details.

The base tweeted Thursday it is on lockdown due to a report of an active shooter. Joint Base Andrews is home to Air Force One.

The tweet instructs all personnel at the base in Washington's Maryland suburbs to shelter in place and says more information will be released as it comes.

Johnson is testifying before the Senate Judiciary Committee. He says he may have to take a break from the hearing as the situation at Andrews develops.