I encountered this caterpillar in North Vietnam (Hanoi) and could not find any reliable web site for this kind of search. I am not an entomologist, so I don't even know how to describe it, except that it has hairy head stalks. I hope my pictures will help. Thanks to anyone who can help me here.
My comment above is actually likely wrong.
Instead, I think this is possibly the larva of the rose-myrtle lappet moth (Trabala vishnou) in the Lasiocampidae. (It may also be the larva of the closely-related roseapple caterpillar, Trabala pallida -- see here and here).
I don't know this group of moths at all, but a series of failed "Lymantriinae" searches and otherwise successful image searches led me to this genus and these species. Lack of reputable resources available in English online make differentiation between species in this genus very difficult for me. Below are some images of Trabala caterpillars:
Images Source: Koh Chang Nature
You can see a very smilar image to the ones above on flickr.