Speculation includes talk that Apple introduce three new iPhone models, infusing some with features from a premium iPhone X that debuted last year with a $1,000 price tag.

In typical enigmatic style, Apple offered scant clues to what it has in store for the presentation to take place in the Steve Jobs Theater at its spaceship campus in the Silicon Valley city of Cupertino.

Invitations had the words "Gather round" under a large golden circle.

Apple has historically held September events to show off new iPhone models, and this year the company is expected to stay true to that course.

Speculation includes talk that Apple introduce three new iPhone models, infusing some with features from a premium iPhone X that debuted last year with a $1,000 price tag.

Apple's event comes a month after smartphone leader Samsung unveiled its latest flagship handset, the Galaxy Note 9.

Although the California tech giant is the world's most valuable company with a market capitalization that recently topped $1 trillion, it has slipped to third place in the global smartphone market behind Chinese-based Huawei, according to surveys.