An envelope containing a white powdery substance was found at the New York Times building Thursday afternoon, officials said.

The mysterious letter was discovered in a basement mail room around 1:30 p.m., prompting police to evacuate a portion of the 52 story skyscraper at 41st St. and 8th Ave. while they investigate.

The person who opened the powder-filled envelope was taken to an area hospital as a precautionary measure.

It’s not clear who the letter was addressed to, police said.

The incident is still under investigation, police said.