The Huffington Post, Gawker, Buzzfeed and many other sites were affected after Datagram, a New York firm that provides corporate Internet connections and servers, said its offices were flooded by "superstorm" Sandy, CNN reported.
Datagram's offices are at the southern tip of Manhattan in an evacuation zone that was one of the worst-hit areas in the city.
The Huffington Post's site was down Tuesday morning, but it automatically redirected to a company blog.
"We are working around the clock to get the site back to normal," the site said, and it came back online about noon EDT.
Gawker remained unreachable.
BuzzFeed was able to get its site back up online Tuesday morning, but was unable to update its website and directed readers to its Tumblr page.
On its Tumblr page, the company said Datagram reported its basement was flooded with 5 feet of water.