UPDATE: The lock down has been lifted at the Capitol.
The US Capitol Police is telling NBC News there is an injured Capitol Police Officer, information on the officer's injuries and how the officer received them have not been released. An NBC employee said there were 10 or 15 gunshots in rapid succession.
People standing outside the Supreme Court across the street from Congress were hurried into the court building by authorities.
In a notice distributed by email, the U.S. Capitol Police advised everyone to "close, lock and stay away from external doors and windows.The notice said gunshots have been reported on Capitol Hill. There are unconfirmed reports of an officer injured.