A firefighter works at Breezy Point in the New York City borough of Queens, Oct. 30, 2012. [Xinhua]

Superstorm Sandy has killed at least 29 people and knocked millions out of power across the densely populated U.S. east coast, leaving streets flooded, houses burned and a levee collapsed by Tuesday morning.

Sandy, which made landfall in New Jersey early Monday evening and combined with winter storms to become a hybrid storm, has impacted 15 states. Sandy so far killed at least 29 people in eight states, according to CNN report, including 15 in New York and three in New Jersey, two of the hardest-hit area overnight. Other U.S. media outlets even put the death toll up to 33 to 35.

The death toll has risen to 10 and may continue to rise in the largest city of the country, New York city Mayor Michael Bloomberg said Tuesday at a press conference.

"This was a devastating storm, maybe the worst that we have ever experienced," said Bloomberg.

About 7 to 8 million customers across eight states have been knocked out of power by the superstorm, according to U.S. media reports.

U.S. President Barack Obama on Tuesday declared "a major disaster" in the states of New Jersey and New York, ordering federal aid to supplement state and local recovery from Sandy.

West Virginia Governor Earl Ray Tomblin later announced that his request for a presidential emergency declaration for the state has also been granted.