this is one of the most common of the hornets, it is the Lesser Banded hornet (Vespa soror)
The good news is that hornets are not aggressive...unless you mess with their next that is! If they nest in a tree, like this nest from Vespa velutina, the nest can get quite large, like in the picture below, that i found in Sai Kung.
The nests have a lovely swirling pattern, but these usually remain empty over winter as the colonies typically die off with the arrival of colder weather around November. However, look for them again in the New Year from March as they look like upside down pots, and then they grow into a ball like the picture above. They prey on small insects but also scavenge, on dead animals and human food. Good vision swift flying and an aggressive defensive strategy means they should be left well alone. (there are recorded fatalities in Taiwan, Malaysia and Indonesia). The nests can have several thousand wasps, sometimes even over 10,000 in hte largest nests.
Vespa soror, as no known common english name. here they are taking nectar, but are aggressive hunters even feeding on geckos. the earliest hornet to emerge and the last to disappear, and can be found even in December.