Apple Inc CEO Tim Cook kicked off an event at which the company is expected to introduce the fifth version of its iPhone.

Cook, an operations and supply-chain expert not known for pitching products, appeared at the event at Apple's headquarters in Silicon Valley, standing in for ailing co-founder Steve Jobs in his new role as chief executive.

A new iPhone would come at a critical juncture as Android phones by Samsung Electronics and other competitors close in on Apple's lead. Android phones dominate the U.S. market three years after Google Inc introduced the mobile software.

Cook, who said Apple controls 5 percent of the global smartphone market, is expected to introduce the latest iPhone later on Tuesday. Wall Street and industry insiders will scrutinize his performance to see if he can carry off a high-profile Apple launch.

Some shareholders and analysts expect a cameo appearance by Jobs, now chairman. The pancreatic cancer survivor, who handed the reins to Cook in August after taking his third medical leave, has not yet appeared.

Apple launches are some of the hottest events on the tech calendar. Tuesday's Let's talk iPhone show marked Cook's unofficial debut since taking over from Jobs in August.

The new iPhone, expected to be faster, thinner and equipped with a larger screen, is likely to come loaded with the updated iOS5 software that Apple unveiled in June. Some of the new features include improved notification functions and better Twitter integration.

The iPhone, which accounts for more than 40 percent of Apple's sales, has been a big success since it came out in 2007, making Apple into one of the world's leading consumer electronics companies.

INTENSIFYING COMPETITION

The company's shares were holding steady at about $373 after rising about 1 percent in the morning.

Apple would be launching the latest version at a time when the economy is slowing and competition is intensifying. More than 550,000 Android-based devices -- including tablets -- are activated each day.

Apple faces the challenge of sustaining the popularity of its iPhone 4, more than a year old. Apple sold more than 20 million units in the third quarter, which ended June 25.

Nielsen data shows the iPhone was No. 2 in the United States with a 28 percent market share, with Android at 43 percent.

Globally, iPhone shipments climbed 9.1 percent in the second quarter while Nokia's plummeted more than 30 percent, handing the top spot to Apple with a market share of 18.4 percent, according to IHS iSuppli.

But Samsung, whose shipments grew even faster, is coming on strong with a global market share of 17.8 percent.

Some on Wall Street also expect Apple to unveil later on Tuesday a cheaper phone for the fast-growing Asian market, one of the areas where Apple can accelerate its growth.

Apple also claims inroads into a corporate market dominated by Research in Motion. It said more than 90 percent of Fortune 500 companies are testing or using its iPhones and iPads.

(Additional reporting by Noel Randewich. Writing by Edwin Chan. Editing by Phil Berlowitz and Robert MacMillan)

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