A MySpace spokesperson said: "Due to the record breaking heat in Los Angeles over the weekend the area where MySpace's servers are stored had massive power outages.

"With power resumed, the network is now up and running."

The spokesman said backup generators at the data centre had failed.

Earlier in the day visitors to the website were greeted with a game of Pacman and a message saying the service hoped to be back up and running within the hour.

The website was bought by Rupert Murdoch's News Corp for $580m last July after it proved to be a huge success with youth audiences online.

The closure of the service, albeit temporarily, will be a blow for News Corp and MySpace in such a competitive environment.

Bebo, one of MySpace's keenest rivals, has been catching MySpace in terms of audience numbers in recent months.

A number of MySpace users posted comments on other blogging services - such as Live Journal and Wordpress - about the temporary closure of the site.

Vanessa Evans, sales and marketing manager at internet infrastructure firm Linx, said companies typically took steps to ensure a power outage would not topple a website.

"Data centres usually have the ability to connect to at least two power sources so that they can switch in case one source is lost.

"I would be surprised for any large company taking space on a data centre which did not have this option."

Yahoo

Ms Evans said that while she could not comment on the MySpace problem directly, she said many companies hosted information at more than one data centre.

Meanwhile, UK users of Yahoo! were without a number of services, including e-mail and instant messenger, on Sunday due to a power failure.

A spokesman told BBC News: "Yahoo! search, Yahoo! Mail and Yahoo! Messenger were quickly restored to normal operation as were many of our content services."

"The remaining services are returning to normal now. We apologise to any of our users who may have been inconvenienced."