An unidentified official said the evacuation was standard procedure. "A climber has been spotted", an official told AFP.
Authorities would not say how the trespasser managed to get past the Eiffel Tower's stringent security system.
A member of the Paris police said a climbing specialist and a team of firefighters were on the scene and were in touch with the intruder.
The esplanade underneath the monument was also evacuated, as was a large section of the adjacent Champ de Mars park.
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Police reportedly have made contact with the climber, though his motives are not yet known.
It's not the first time when a man attempts to climb the tower.
The closure comes less than one week after the Eiffel Tower celebrated its 130 anniversary with an elaborate light show.
Almost seven million people a year visit the tower, which last week celebrated its 130th anniversary.
In 2015, adventure blogger James Kingston and a friend scaled the landmark at night, recording with a GoPro camera as they ascended.
The first two floors can be reached by either elevator or stairs, but only elevators can take visitors to the top observation deck.