The Apple smartphone brand will remain on top of the food chain following the September release date of the iPhone 5S, a new report said.

Research firm Detwiler Fenton has forecasted a steady sales figure for the tech giant despite impressions that the iPhone 5S debut this fall will encounter rough roads, primarily due to the strong start of Samsung's Galaxy S4.

To date, the GS4 has amassed more than 10 million buys and analysts expect the number to further soar in the months and quarter ahead.

Detwiler's Mark Gerber has acknowledged that Samsung is gaining fast on Apple, which is a trend that started last year via the Galaxy S3 but the sales growth it has accumulated is not enough to overwhelm the iPhone maker anytime soon.

"Samsung's GS4 has sold well but with it only up roughly 15 per cent over GS3 sales in North America," Mr Gerber was quoted as saying by Barron's in a new research note.

The analyst said that overall iPhone sales for the June quarter will reach 33 million units, a testament, he added, to the resilient Apple brand, which is also extended to the iPad 5 and iPad Mini 2 - both rumoured to rollout shortly after the iPhone 5S release date in September.

For the refreshed Apple smartphone, "our latest checks continue to indicate ... iPhone sales remain resilient," Mr Gerber said, noting too that the indicators used are focused in the North American region, currently one of the most lucrative mobile device markets.

Apart from relying on its established brand and distribution muscle, Apple will also count on the new killer features that the 5S will bring to the table, analysts said.

One of them, according to Engadget, is the radio streaming services called iRadio. It is likely that this feature will be unveiled in time for the WWDC event next month as Apple reportedly sealed a deal with music producers Warner and Universal recently.

However, the tech giant's negotiations with Sony remains deadlocked, pointing to one missing link that would allow Apple to match Google's Play Music, which is also available to iOS device users.

On its launch date, the iPhone 5S is expected to present jaw-dropping capabilities that analysts termed as killer features. Among them are Retina+ or Retina HD, which delivers 1.5 million pixels, fingerprint sensor, LED notification and 12MP cam shooter with emphasis on dual shots..

Also, Apple will reportedly sell the iPhone 5S in numerous colour options, deviating from the usual black and white cases.