Staff working at the US Capitol were told to stay inside and away from windows on Tuesday morning due to an "external security threat" under a nearby bridge.
The incident turned out to only be a small fire, but it's underscored the level of anxiety in Washington DC after this month's deadly Capitol riot.
US media reports that an alert was sent to people inside the Capitol, warning them not to enter or leave any of the complex's buildings due to an "external security threat under a bridge". Photos show participants in an inauguration rehearsal outside the Capitol were evacuated inside.
The Secret Service later confirmed that authorities had been responding to a fire, which has now been extinguished.
"Out of an abundance of caution the US Capitol complex was temporarily shutdown. There is no threat to the public."
It comes less than two weeks after the storming of the Capitol by pro-Donald Trump insurrectionists. At least five people died during that violent riot.
Authorities are currently on high alert ahead of Joe Biden's inauguration on Thursday (NZT).