As Dave says there was one of these at Mai Po last year, and I think the year before too.
However, there are a couple of features which do not fit Brown-chested Flycatcher.
One is the all-black bill and the other is the rather long tail (although this may simply be the angle)
I think this is a rather early female Blue-and-white Flycatcher, which has an all-black bill large eyering and can show a reddish tail.
Cheers
Mike K
Mike KilburnVice Chairman, HKBWSChairman, Conservation Committee