"The demand supply balance is already very tight," Economy, Trade and Industry Minister Banri Kaieda said in a statement.

"If this situation continues, demand will far exceed supply todayfrom the evening to night when daily power demand peaks, and unpredictable major blackouts are feared," he said in a statement.

Prime Minister Naoto Kan said Sunday he had authorised managed outages to prevent any sudden major supply disruption, as electricity supply has fallen sharply since the quake tsunami disaster hit power plants on Friday.