WASHINGTON – The U.S. Capitol complex was briefly locked down and an inaugural rehearsal at the West Front of the U.S. Capitol was evacuated Monday after a fire in a homeless encampment, authorities said.

"Out of an abundance of caution the U.S. Capitol complex was temporarily shut down," the Secret Service said on Twitter. "There is no threat to the public."

The lockdown lasted about an hour. President-elect Joe Biden was not present.

The incident occurred as the nation's capital is on edge days before Biden's inauguration and two weeks after a violent riot at the Capitol by supporters of President Donald Trump who believe falsely that the election was rigged.

The rehearsal was taking place at the Capitol's West Front when Capitol Police began yelling to "get inside" and "this is not a drill." Scores of people began running up the steps, some struggling to ascend them, as an automated announcement told those fleeing of an "external threat."

D.C. Fire officials said they responded to a fire near the Capitol "that has been extinguished. There were no injuries. This accounts for smoke that many have seen."

The fire in a homeless tent beneath a nearby freeway was extinguished, fire officials said. The occupant was using propane, which could explain a report of an “explosion," they said. One person was treated for non-life-threatening injuries.

Lawmakers in all buildings within the Capitol complex were warned that "due to an external security threat located under the bridge on I-295 at First and F Streets SE, no entry or exit is permitted at this time."

Lawmakers and staff were told that they could move through their buildings but were warned to "stay away from exterior windows and doors. If you are outside, seek cover.”