News anchors interrupted their bulletins on national networks France Info and France Inter as the order to evacuate the building came through.
Hundreds of journalists, technicians and other staff assembled on an island in the middle of the River Seine as thick smoke bellowed out of the top three floor of the huge eight-story building.
The heat caused several windows to explode but nobody was reported injured.
Sixteen fire engines were rushed to the scene and France Info was able to restart broadcasts from an emergency studio shortly after 2.00pm with the fire under control although not extinguished.
Police limited traffic in the streets around the building and on the major road heading for central Paris along the side of the river.
The fire is reported to have started in an area where building work was being carried out.
The gigantic, circular Maison de la Radio is a Paris landmark, built 50 years ago.
It has been being renovated since 2009 in the biggest renovation scheme of a building while in use in France.
The work is scheduled to be completed in 2016.
A new 1,460-seat auditorium with state-of-the-art acoustics was due to be opened to the public on 14 November.
The fire is an "extremely traumatic event", French President François Hollande commented during a joint press conference with visiting Turkish President Recep Tayyip Erdogan, adding that it was a "symbolic" building.
"I am watching this very carefully," the French president said.
RFI was based there from its creation in 1975 until January 2013, when it moved to the Paris suburb of Issy-les-Moulineaux.