iPhone 5S production has already kicked off, a Japanese-language Apple blog reported today.
The 5S is being built on the same production line as the iPhone 5, according to Macotakara.
The Japanese blog goes on to claim that NTT Docomo is cutting back on orders for Android devices to make way for introduction of the iPhone. NTT Docomo does not currently carry the iPhone.
Whichever it is, it would make sense for limited production to begin in March.
The 5S may use a new A7 Apple chip, a better camera based on a LED technology referred to as "Smart Flash, a fingerprint chip, and versions will support China's time-division duplexing (TDD) standard, according to recent speculation.