Usain Bolt: I HAVE ARRIVED ... Touches Down In Rio

Behold ... BOLT IS IN BRAZIL!!!

The fastest man EVER landed in Rio Thursday morning -- and greeted the fans with an "I am here" pose.

Bolt was greeted by fans and media -- but didn't say a word ... just gesturing with his hands before being whisked off in a private car.

Bolt's gunning for a "triple-triple" at the 2016 Games -- looking to win gold in all 3 of his events (100m, 200m and 4x100m) for the 3rd Olympics in a row.

But Team USA sprinter Justin Gatlin says he ain't gonna let it happen -- telling "TMZ Sports" he "guarantees" victory over his Olympic rival.

Should be fun!!!