From the tweet:

A new Chinese 500 tons displacement Combat USV (Unmanned Surface Vehicle) arrived at Doumen, Zhuhai. This USV is armed with 4 vertical launch cells (VLS), close in weapon system (CIWS), advanced radars and Electronic Warfare censors and a landing pad at the rear supporting a VTOL UAV.

In other words, this is a unmanned missile boat, of which 24 equals one magazine's worth of an Arleigh-Burke Destroyer. Probably just tech demonstration or intended for export at the moment.