HONOLULU -- The mayor of Honolulu, Mufi Hannemann, said about 50 percent of Oahu's power has been restored after a power blackout hit all of the main Hawaiian island, including the vacation rental home of President-elect Barack Obama.

The mayor told the Associated Press that the blackout, which started at about 6:45 p.m. Friday, would last more than 17 hours for some residents.

Power went out for 900,000 Oahu residents and tens of thousands of tourists.

The blackout came during a thunderstorm. Hawaiian Electric Co. is investigating the cause.

While he did not talk with Obama directly, the mayor said he conveyed an offer for assistance and was told the president-elect and his family were doing fine and didn't need anything more.