The sisters from southwestern China arrived in Hong Kong on a recent holiday, aiming to see as much as they could — in less than 12 hours.

Carrying only a small bag each, Hu Di, 30, a bank worker, and Hu Ke, 20, a student, sampled beef noodles in the Central business district, took turns posing for sunset photos at a waterfront promenade, then captured the city’s illuminated skyline after dark. Buying only medicinal oils and retro comics as souvenirs, they spent less than $150 in the day and went back across the mainland China border to stay the night.

The sisters are part of a wildly popular trend among mainland Chinese who call themselves "special forces tourists”: independent travelers who get in and out of the city as quickly and cheaply as possible.