It is 4 a.m. in a deserted area of downtown New York.

Suddenly, a manhole cover opens, and people crawl out one by one.

They are wearing matching jumpsuits and headlamps on their heads.

It remains unknown what they were doing underground in the early morning hours.

A similar sight was captured in the same area last May.

At the time, authorities deployed an emergency response team to conduct a search, but failed to identify who they were.

Some suggest they could be "treasure hunters" searching for valuables washed down into the sewers.

(Video source: TikTok @ricardyfabre)