What's the point of adding "đang" to this? Unless there were a different tense inserted, I'd assume "Tôi ở đây" to be present continuous.
Hmm it seems trickier. Thai yuu means "be at/located" and Chinese zai has that same meaning. But Chinese zai also means "-ing" where Thai does not use the same word but instead uses gamlang. In the dictionary, Vietnamese đang means "-ing" but in this question it seems to function more like "be at/located"...