An apparent smoke bomb was thrown over the fence of the White House as hundreds of Occupy protesters massed outside the gates.
The crowds were dispersed and US Secret Service spokesman George Ogilvie said there were no arrests in the incident.
However, people inside the White House were prevented from exiting on the Pennsylvania Avenue side of the building as the situation was being resolved.
US President Barack Obama and his wife, Michelle, were at a nearby restaurant celebrating her 48th birthday at the time of the incident.
Mr Ogilvie said there were 1,000 to 1,500 protesters at one point.
He said something which appeared to be a smoke bomb was thrown over the fence and that the device was being removed.