The first edition of the Nyansapo Festival, due to run from July 28 to 30 at a cultural centre in Paris, bills itself as "an event rooted in blackfeminism, activism, and on (a) European scale."
Four-fifths of the festival area will be set aside as a "non-mixed" space "for black women," according to its website in French.
Another space will be a "non-mixed" area "for black people" regardless of gender. Another space would be "open to all."
The English version of the site does not use the word "non-mixed," but "reserved."
Hidalgo (photo above), a Socialist, said on Twitter that she firmly condemned the organisation "of this event, 'prohibited to white people'."
"I am asking for this festival to be banned," Hidalgo said, adding she also reserved the right "to prosecute the organisers for discrimination."
Police prefect Michel Delpuech said in a statement that police had not been advised about the event by Sunday evening.
But, Delpuech added, the police "would ensure the rigorous compliance of the laws, values, and principles of the republic".
French antiracist and antisemitism organisations strongly condemned the festival.
SOS Racisme described the event as "a mistake, even an abomination, because it wallows in ethnic separation, whereas anti-racism is a movement which seeks to go beyond race."
LICRA -- the International League against Racism and Antisemitism -- said "Rosa Parks would be turning in her grave," a reference to the American civil rights icon.
Wallerand de Saint-Just, the regional head of Marine Le Pen's National Front party, had challenged Hidalgo on Friday to explain how the city was putting on an event "promoting a concept that is blatantly racist and anti-republican."
The cultural centre La Generale, where the event was to be hosted, and the collective Mwasi, which organised the event, said Sunday they were the "target of a disinformation campaign and of 'fake news' orchestrated by the foulest far right."
"We are saddened to see certain antiracist associations letting themselves be manipulated like this," according to a statement posted on the Generale website.
A "decolonisation summer camp" in the northeastern French city of Reims elicited similar outrage last year, as it billed itself as a "training seminar on antiracism" reserved for victims of "institutional racism" or "racialised" minorities -- excluding by default white people.