Power utility Eskom on Wednesday called on consumers to switch off geysers, pool pumps and all non-e.
National bakers association vice president Antonio Arias says the bready Rosca de Reyes was estimated to be sliced into 200,000 pieces.
Bakers used more than 5 metric tons of flour, 3 tons of butter and 38,600 eggs to create the cake.
The sweet bread is traditionally eaten on Jan. 6, Three Kings Day, marking the end of the holiday season in Mexico.
The 1 1/2-kilometer-long cake was decorated with dried fruits and hidden inside were non-edible plastic figures of the baby Jesus.