What a beauty ! This is Camacinia gigantea, which looks like several Neurothemis species but is much bigger.
I sighted this species only one time. It was in mid-April and I was searching... migrant birds in the Lenin Park, the largest green space in inner Hanoi. There is a big lake there, but the banks have been entirely cemented over. This park has really nothing to offer to dragonflies, even to the most common and ubiquist of them.
In a dry bushy area, I noticed a big Libellulid resting in a vertical position. I managed to get some shots with the 400 mm lens (no macro lens in the bag...), and for that I had to step back 4-5 meters!
Few days later, I came back to get better shots but failed to find it gain.
What the hell this guy was doing there! If it was a bird, "escaped from a cage" would have been my first thought. But a dragonfly...
Camacinia gigantea is very similar to Neurothemis fluctuans, and it can easily be mistaken. One significant difference is the large size of Camacinia gigantea. It attains 53–56 mm in total length, and is reputed to be the largest dragonfly in the family Libellulidae. In contrast, Neurothemis fluctuans is 30–34 mm in total length. The red colouration on the wings of Camacinia gigantea almost covers 2/3 of its wing while in Neurothemis fluctuans, the red colouration is much more extensive, covering approximately 4/5 of its wing and attaining the pterostigma.
Camacinia gigantea is widely distributed from India to Vietnam and southwards to New Guinea.
This species appears to be somewhat local but can be common where it occurs.