WASHINGTON — The US Capitol was on lockdown on Monday just two days before the presidential inauguration following an explosion at a nearby homeless camp.

People were seen rushing away from the rehearsals for the swearing-in of Joe Biden, which is due to take place this Wednesday.

Videos of the Capitol show smoke rising above the Washington D.C. building, which was broken into and vandalized earlier this month.

A loudspeaker system that boomed out across the city could be heard warning people of an “external security threat”.

No one is allowed to enter or exit the building, where people are being forced to shelter inside.

The Capitol Police said there was a “small explosion” at a homeless camp on First and F Streets SE.

"The incident has been contained, however, staff and other personnel are directed to continue to avoid coming to the Capitol Complex area until further notice," the force said in a statement.

The District of Columbia Fire and Emergency Medical Services Department tweeted: "#DCsBravest responded to an outside fire in the 100 block of H St SE that has been extinguished.

"There were no injuries. This accounts for smoke that many have seen."

The US capital has been on high alert since Donald Trump supporters raided the Congressional building on Jan. 6.

Security has been hugely ramped up since the storming, which claimed the lives of five people.

Many of the rioters called for the death of Vice President Mike Pence as he presided over the certification of Joe Biden's election victory. — Agencies