Apple Inc unveiled the "Apple Watch" alongside two new iPhones with sharper and larger displays on Tuesday, calling the wearable device the next chapter in its history.

The first new product to be developed and introduced under Chief Executive Officer Tim Cook's reign is a wearable device tethered to the iPhone that will combine health and fitness tracking with communications.

Bernstein Research analyst Toni Sacconaghi estimated on Tuesday that if Apple were to sell 30 million watches at $250 each, it would add about $7.5 billion to its revenue.

Rival electronics giants such as Sony Corp, Samsung, LG Electronics Inc and Qualcomm Inc have already launched smartwatches, albeit without much success.

The pressure had been on for the world's largest tech company to wow at its "special event" in Cupertino. The prospect of the Watch had attracted a broader swathe of attendees than usual, with celebrities, fashion industry editors and even healthcare executives rounding out the mostly tech-industry crowd.

On Tuesday, the company took the wraps off a larger, 4.7-inch iPhone 6 and 5.5-inch iPhone 6 Plus. They will support more than 200 telecoms carriers worldwide, including all three in China -- a key growth market for the company.

It also introduced a new mobile payments service dubbed "Apple Pay." Each phone will come equipped with its new payments service, which launches in the United States next month and allows users to pay for items in stores with their phones instead of physically presenting their credit or debit cards.

In a rare move for the company, Apple had planned on livecasting its event online, with a simultaneous translation in Chinese. But the livestream went down for many users about a half-hour in, prompting many to take to Twitter to express their frustrations.

Apple stock volatile

Apple Inc was sharply higher in afternoon trading on Tuesday, moving on heavy volume as the company unveiled a new smartwatch, an item representing a new product category, as had been widely expected.

The stock was one of the S&P 500's biggest gainers on the day, advancing 3.2 percent to $101.56 in its biggest one-day move since April 28. Volume of about 109 million shares was more than double its 50-day average of 49.1 million.

Apple says will not store credit card info, Apple pay will use a one-time payment number and security code each time a user pays

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