Office workers stayed at their air-conditioned desks while lights on the Brooklyn Bridge, the Empire State Building and the halls of Congress in Washington were dimmed to save power.

But despite these efforts to reduce power consumption, electricity suppliers in New York, Washington and across the Mid-Atlantic and Midwest reported new demand records, which surpassed the highs set on Tuesday.

New York Mayor Michael Bloomberg -- hoping to avoid a blackout such as the one in 2003 which saw New York City's 8 million residents and 50 million people in US Northeast go without power -- pleaded for New Yorkers to cut their electricity use at home as the city prepared to face a third straight day of 100-degree F  (38-C) temperatures on Thursday.

''(The problem is) in the residential neighborhoods. If we want to keep the power going we're all just going to have to have to conserve,'' he told reporters, adding that the city's electricity grid was under ''great strain.''

Only minor power outages have been reported in cities like Chicago and New York. That helped boost utility shares and the Dow Jones Utilities average touched an all-time high on Wednesday.