The second-generation of Microsoft Surface tablets, the Surface 2 and the Surface Pro 2, could be a secret holiday hit as both the devices have sold out across various stores in the U.S.

The tablet market is growing rapidly and tablet shipments may beat PC shipments in the coming few years. To keep pace with the current market conditions, Microsoft announced the launch of its first line of Windows tablets in June 2012. The company released the Windows RT tablet in October 2012 and the Surface Pro in February 2013.

Even though the tablets were relatively popular in the tablet space, sales for both the Surface RT and the Surface Pro were disappointing and behind Microsoft's own expectation. The company also revealed that it had made a loss with the tablets as marketing costs exceeded the sales. Microsoft also had reduced the price of both the tablets to attract more customers.

However, it seems that the company has done it right with the release of the second generation tablets in October this year and reports suggests that both of them have sold out across various retailers in the country.

"The old Surface sold very poorly. By the time they did specials on it, we were well out of the buying season," said Rob Enderle, principal analyst with the Enderle Group. "This one appears to be doing much better than the old one."

Surface 2, which has a price tag of $449 for the 32GB version and $549 for the 64GB, is currently out of stock on Microsoft Store. Similarly, the 64GB/256GB/512GB versions of the Surface Pro 2, which is priced at $899/$1299/$1799 are also out of stock on Microsoft Store. Only the 128GB model is available at the company's online store.

Amazon.com has just a few units available, which may get sold sooner than later. Walmart also does not seem to have the Surface 2 in stock but has the 128GB model of the Surface Pro 2 in stock.

Mashable reported it contacted several Best Buy stores in different locations but all reported that the second-generation Surface tablets are out of stock.

Many customers have also tweeted regarding the lack of availability of the Surface tablets.

"The @Surface 2 is sold out everywhere... even Microsoft's own store. Are people actually... gasp... buying Surface 2s?!?!?" tweeted one user.

The @Surface 2 is sold out everywhere... even Microsoft's own store. Are people actually... gasp... buying Surface 2s?!?!?

— Marc Chambers (@marcchambers) December 14, 2013

With the first generation Surface tablets, Microsoft faced the problem of getting them off the shelves. Now, with the second generation Surface tablets, it seems Microsoft is facing a different kind of problem - keeping up with unprecedented demand. And, we're certain Microsoft is loving it.