Estimates based on early results suggest right-wing UMP candidate Kosciusko-Morizet is leading with around 35.2% to 35.9% of the vote, closely followed by current deputy mayor and Socialist candidate Hidalgo on 34% to 34.4%.
The Greens candidate, Christophe Najdovski, appear to win less than 10% of the vote, meaning he and other candidates will be ruled out of the second-round next Sunday, according to electoral law.
The Greens are likely to support Socialist Hidalgo in the second round.
Kosciusko-Morizet, affectionately known as NKM, is a former minister under President Nicolas Sarkozy. Hidalgo has been the deputy mayor since 2001 under outgoing mayor Bertrand Delanöe.
NKM said her party had “one week to win over Paris”.
“Never before has change been so close,” she told party faithfuls as the first results came in.
She has promised to “restore dynamism” to Paris, and “make it a city that people don’t want to leave”, making reference to the growing number of young people who have chosen to leave the capital for overseas, particularly London, to work and start new businesses.
Hidalgo, who had been tipped as the favourite before the polls, was visibly more disappointed than NKM when addressing her supporters, calling for a “second mobilisation” in all districts in Paris to win over voters.
The local elections were the first major test for the struggling Socialist party since President François Hollande’s election in 2012.
Although the elections are not directly linked to national politics, right-wing parties had urged the electorate across France to punish the Socialists and Hollande over their management of the country.
“I know the national context is difficult,’ Hidalgo said, “but [the left’s] innovative force is still here.”
Delanöe congratulated Hidalgo’s performance and called on “all Parisians, whatever their persuasion, to vote next Sunday.”
Among their election promises, Hidalgo promised no new taxes during her first term, and suggested more floating swimming pools on the Seine River.
NKM promised to turn disused metro stations into swimming pools, performance spaces and restaurants.