About 64,000 households are still without electricity in Chiba Prefecture, near Tokyo, more than a week after a typhoon struck the area.
Typhoon Faxai made landfall in the prefecture on September 9, causing extensive damage. Tokyo Electric Power Company is rushing to repair the grid, but work is facing delays in some areas.
TEPCO had estimated that the number of households without power would drop to fewer than 100 in the Wakaba district of Chiba City by Monday.
But 500 households still lack electricity, as work to remove fallen trees is taking longer than expected.
TEPCO says that in some cities and towns, restoring power may take well over another week, until September 27.
Even in areas where the lights are back on, the utility is warning residents to be alert to the risk of fire caused by electric wiring that was damaged in the storm.
The company is urging people who are still without power to turn off the circuit breakers if they are leaving their house for long periods.