The touch-screen device was billed by Google as a "superphone" and the next step in the evolution of its Android software.
The Internet giant worked with Taiwanese electronics titan HTC to make the Nexus One.
"I think you will see it pushes the limits of what's possible on a smart phone," HTC chief executive Peter Chou said as the smartphone was unveiled at Google headquarters in Mountain View, California.
"It is very thin and feels good in your hand," he added.
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Nexus One handsets are no thicker than pencils and no heavier than keychain Swiss Army knives, Google engineer Erick Tseng said while demonstrating one of the smartphones.
Android software
"It is a great marriage of form and function," Tseng said. "It is really light."
Nexus One smartphones are built on the same Android 2.1 software that runs Droid smartphones that recently hit the market but feature innovations including 3D graphics, according to Tseng.
Google said it is launching "in a few minutes" its own online store at which the Nexus One will be sold.
Nexus One smartphones will be sold at the Google-hosted web store for $US529 ($A578) "unlocked," without ties to a telecom carrier.
Nexus One handsets will be offered at prices starting at $US179 ($A196) if paired with T-Mobile service contracts in the US.
Google has made "strategic partnerships" with telecoms firms Verizon in the United States and Vodafone in Europe.
Nexus One devices linked to service from Verizon in the US and Vodafone in Europe should be available by mid-year, according to Google.
Google said it will ship Nexus One devices to buyers in Singapore, Hong Kong, Britain and the US.
