Apple on Tuesday invited members of the media to a September 12 event in San Francisco for what is expected to be the debut of a new-generation iPhone.

Email invitations bore the cryptic message, "It's almost here," and a large number "12" casting a shadow that appeared to be the number five, suggesting that the event would spotlight the long-anticipated iPhone 5.

Leaks and rumors portray the new iPhone as having a larger touch-screen than its predecessor and say that it will be available by the end of the month.

Demand for what is being referred to as "iPhone 5" is likely to be hot, with analysts convinced that many people in the market for handsets have put off purchases to wait for the latest offering from Apple.

"While our checks indicated consumers are delaying iPhone 4S purchases in anticipation of the iPhone 5, we anticipate an LTE iPhone 5 with a new hardware form factor will result in record iPhone sales," Canaccord Genuity brokerage firm said in a note to investors.

Apple shares ended the official trading day at $674.97 and then inched up to $675.25 in after-market trades.

Samsung mobile phones remained the most popular in the United States with 25.6 percent of the market, but third-place Apple gained ground to claim 16.3 percent as of the end of July, according to industry tracker comScore.

LG ranked second with 18.4 percent of the US mobile phone market.

Smartphones powered by Google's Android software continued to dominate with 52.2 percent of the US market, but Apple's iOS was the second most popular smartphone platform with 33.4 percent, comScore reported.

Apple is expected to host a separate media event in October to unveil a new, smaller version of its wildly popular iPad.

The 10-inch iPad has long dominated the tablet market, but faces a growing challenge from smaller models like Amazon's Kindle Fire, the Google Nexus 7 and the Samsung Galaxy.

Analysts believe Apple will launch an "iPad mini" later this year in a move that could allow the company to again best its global rivals despite the death last year of visionary founder Steve Jobs.

Microsoft, Google and Amazon.com are out to grab spotlights ahead of the Apple event with announcements of their own this week.

Nokia and US giant Microsoft are hosting a media event in New York City on Wednesday, most likely to launch one or more smartphones using the Windows Phone 8 operating system.

Nokia on Tuesday unveiled a free music streaming service for US customers with its Lumia handsets, without ads, as the firm seeks to gain traction in the smartphone market.

Nokia, once the leader in mobile phones, has been losing market share as consumers move to smartphones powered by Apple's iOS or Google's Android operating system.

The Finnish company's new strategy is phasing out its Symbian smartphones in favor of a partnership with Microsoft.

That alliance has produced a first line of Lumia smartphones, which Nokia is counting on to help it survive in a rapidly changing landscape.

Google-owned Motorola Mobility and US telecom titan Verizon Wireless will host their own New York City event on Wednesday, with analysts predicting they will introduce a beefed-up Razr smartphone powered by Android software.

A day later, Amazon.com is expected to debut a new version of its popular Kindle tablets at an event in Southern California.

Meanwhile, Taiwan-based consumer electronics titan HTC plans a September 19 event in New York City, at which it is expected to unveil slick new smartphones powered by Microsoft's new Windows 8 mobile software platform.