TOKYO — Across the street from Japan’s Diet parliament building, with its pyramid-shaped dome, stands the prime minister’s official residence. Completed in 1929 and serving also as the prime minister’s office until 2002, the art deco structure is now bustling with workers as it undergoes renovations to welcome a new occupant.

Officials explain the historic nature of the grand structure means renovations will take time. With this year’s major work still unfinished, including seismic retrofitting to protect the building in earthquake-prone Japan, there is no clear indication of when the next occupant will be able to move in.