A salesman at the Best Buy retail store in New York's Union Square, which is open 24 hours, said the TouchPad attracted a small line when it went on sale there at midnight, and that 20 of the devices had been sold by 8 a.m. A salesman at Staples in New York's Flatiron district said the device won't go on sale there until Saturday.

The TouchPad enters a market dominated by Apple's iPad, and which also includes Research In Motion's Playbook and a panoply of Android tablets from numerous vendors. The iPad accounted for 74 percent of the 6 million tablets that were sold in the first quarter, . Most of the rest were devices based on Google's Android OS, such as the Samsung Galaxy Tab.

The TouchPad could fill a gap left open by all those Android-based tablets, which share similar features and have for the most part been met cooly by customers, said Sarah Rotman Epps, a senior analyst at Forrester Research.

"Android tablets are not selling to the extent OEMs expected. WebOS may be a reasonable alternative," Epps said.

The TouchPad has a 9.7-inch screen, a dual-core 1.2GHz processor and Wi-Fi for connectivity, and is priced at US$499 for a 16GB model and $599 for a 32GB model. It uses version 3.0 of HP's webOS, which it obtained when it bought Palm last year. TouchPad's with cellular connectivity are due at a later date.