3:40 PM PT -- NYPD just got the guy ... yanking him through an open window while he tried to fight the cops off.
A man is scaling Trump Tower in Manhattan as a mesmerized crowd watches below.
The guy is using suction cups to scale the south side of the tower ... cops and firefighters are trying to coax him down.
As for why he's doing what he's doing ... so far, it's a mystery. There are reports he's carrying papers with Trump's name on it.