"The Eiffel Tower has been closed and is in the process of being evacuated because a person is scaling it", a spokeswoman for the landmark said.
A rescue worker, top in red, hangs from the Eiffel Tower while a climber is seen below him between two iron columns Monday, May 20, 2019 in Paris.
The Eiffel Tower, built by Gustave Eiffel in 1889, celebrated its 130th-anniversary last week.
Local media reports show tourists leaving the grounds of the tower while others stand around watching the scene unfold.
The official Twitter account for the Tower announced that it was closed "until further notice".
Visitors were advised to postpone their visit, while those already in the monument at the time the climber was spotted having to stay in on lockdown for a long time.
Police said the climber's motives were not clear and a negotiator was present.
The Irish Independent's Deputy News Editor Claire Murphy tweeted: "Some kind of security incident at the Eiffel Tower". "He started to climb once he was on the second floor", she said.
It has become one of the most popular tourist attractions in the world, with around 6 million people ascending the landmark every year.
In 2015, the tower was scaled by daredevil James Kingston, who did so without any safety ropes or harnesses.