Skype suffered an outage lasting several hours affecting millions of users of the Internet communications service.

"Our engineers and site operations team are working non-stop to get things back to normal -- thanks for your continued patience," Luxembourg-based Skype said in a message on its Twitter feed @Skype following yesterday's outage.

In a blog post, Skype explained that computers known as "supernodes" had been taken offline by an unspecified problem affecting some versions of Skype.

"Under normal circumstances, there are a large number of supernodes available," Skype said. "Our engineers are creating new 'mega-supernodes' as fast as they can, which should gradually return things to normal.

"This may take a few hours, and we sincerely apologise for the disruption to your conversations," Skype said. "Some features, like group video calling, may take longer to return to normal."

Skype, which was founded in 2003, bypasses the standard telephone network by channelling voice, video and text conversations over the Internet.

The company announced plans in August to raise up to 100 million dollars in shares by listing on the Nasdaq stock exchange.

The service has millions of users around the world and many took to Twitter to complain about the outage in a variety of languages.

"Holy crap. end of the world... #skype is down," wrote Rafael Otero on his Twitter feed @rotero.

"Ugh. #skype went down when I was in the middle of a call," said Carly-Anne Fairlie on @carlyannedotcom.

Technology blogger Om Malik, writing on his blog GigaOm.com, said the outage was a serious issue for a company that is "starting to ask larger corporations for their business."

"If I am a big business, I would be extremely cautious about adopting Skype for business, especially in the light of this current outage," Malik said, adding that Skype "needs to ensure that it doesn't go down. Even for a few minutes."