There was high drama Sunday at NYC's famed Brooklyn Bridge, where a naked man jumped from the top of the span and plunged into the East River — and survived!

And get this ... the insane incident was all caught on dramatic video shot by stunned onlookers, who posted the footage to social media.

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NYPD sources tell TMZ ... the 44-year-old man climbed up to the top of the north tower before removing all of this clothes. We're told he was carrying a Kazakhstan flag, which he affixed to the bridge.

Our sources say officers from NYPD's Emergency Service Unit responded and climbed up the north tower to try to talk the man down to safety.

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But it didn't work. As the parties were chatting, the man jumped off the tower, splashing into the East River below.

Luckily, NYPD's Harbor Unit was there to fish the man out of the water. We're told he managed to escape physical injury, which was miraculous given how far he fell ... but he was taken to a hospital for psychiatric evaluation.

Police are reviewing the matter to determine if the man committed a crime and should be arrested.

Crazy stuff!