This is an eagle that you can see all year round in Hong Kong, and this is the wonderful and huge white-bellied sea eagle (Haliaeetus leucogaster), also known as the white-breasted sea eagle.
These typically patrol further offshore, but you can see them high in the sky over sai kung sometimes, in pairs or with young; or you can get lucky sometimes like here, when the bird flew near the pier.
The species is monogamous, with pairs remaining together until one bird dies, after which the surviving bird quickly seeks a new mate. This means that they return to the same nesting sites....near sai kung.
Here a juvenile with darker wings with an adult.