Emergency responders are at the scene in Paris.
The climber, in black, is currently near the top of the 1,000-foot structure. A rescuer, in red, can be seen above him.
"We are being told a guy paid in and then started to climb from the second floor," Claire Murphy, deputy news editor for the Irish Independent, posted on Twitter.
She later added that she and others were evacuated from the landmark. Police said the evacuation was merely a precaution.
It's not known why the person is climbing the tower.