PARIS (AFP) - France's iconic Eiffel Tower was plunged into darkness late on Thursday in a sombre tribute to the 12 people killed in the attack on the Paris satirical weekly Charlie Hebdo.

The lights normally illuminating the 324m tall monument at night were briefly turned off at 8pm (3am on Friday Singapore time) before gradually coming back on.

The symbolic gesture came as thousands of people gathered on the other side of the city in Republique square to hold a second night of vigils in memory of the victims of the worst attack on French soil in decades.

Other events will be held in the French capital in the coming days to mark the outrage over Wednesday's attack on Charlie Hebdo, and to assert the right to freedom of expression - a value France has long cherished and sought to protect.

"Our city has been a refuge for writers, philosophers, journalists who were threatened for their ideas," Paris mayor Anne Hidalgo told Liberation newspaper.

"There is no place in Paris for extremist ideas of any sort."

The Eiffel Tower is one of France's top tourist attractions and the pre-eminent monument in the City of Light.