A flash fire in the ductwork of the State Department injured four people Saturday, including three who were sent to a hospital, fire officials said.

One person was in a "life-threatening condition" and the other two people were in serious but non-life threatening condition at Washington Hospital Center, authorities said.

The fourth person fell from a ladder and hurt his knee, authorities said.

The fire started shortly after 11 a.m., as construction crews were working on the premises, said Lon Walls, a spokesman for Washington's fire department.

Construction workers extinguished the flames before fire trucks arrived, Walls said.

There were few federal employees in the government building because of the holiday weekend, Walls told CNN.