KK is correct that the lack of a white neck ring rules out Kentish and Little Ringed Plovers (and Common Ringed and Long-billed, which in any case are much rarer). This individual is slightly confusing because the back of the neck is pale, which could be confused with the neck ring, but it is still definitely brownish along the neck. So, I agree that this is one of the Sand Plovers in non-breeding plumage.
Sand Plover ID in non-breeding plumage is not easy. Both species share many plumage features, so it is important to look at structure. I recommend anyone to get familiar with the structure of breeding plumaged birds, which helps with ID of non-breeding birds. In the case of this individual, the bill is rather long and heavy-looking with a sharply pointed tip. The body is not held particularly upright and the head seems fairly 'square'. These features all add up to this being a non-breeding plumaged Greater Sand Plover.
Given the time of year, the fact that this bird is in non-breeding plumage and is still at Mai Po indicates that this is a first-summer bird (i.e. hatched in 2012) that will not breed this year.
