The incident occurred on the beach at the city’s Promenade des Anglais, the location of the lorry attack on Bastille Day in which 84 people were killed last month.
Photographs show four police officers armed with handguns, batons and pepper spray standing round the woman who was lying on the beach wearing a blue headscarf and matching top.
After speaking to the woman, she appears to remove the blue long-sleeve top.
She is thought to have been issued with a fine and warned about the new dress code on the beach.
Several women have now been fined in France for wearing the swim wear.
The former air-hostess from Toulouse was issued a ticket saying she was not wearing “an outfit respecting good morals and secularism”.
“I was sitting on a beach with my family,” she said. “I wasn’t even planning to swim, just to dip my feet.”
Mathilde Cusin, a French journalist for France 4 TV, who witnessed the incident, said: “I saw three police officers watching the beach. One of them had his finger on the trigger of his tear gas device, no doubt containing pepper.”
“It was pretty violent. I had the impression of a pack going after a woman sitting on the ground, crying with her daughter.”
“The saddest thing was that people were shouting ‘go home’, some were applauding the police,” she said. “Her daughter was crying.”
On Monday, Twitter user Feiza Ben Mohamed uploaded a video which shows officers patrolling a beach and reportedly waiting for two girls to come out of the water where they were met by police in Nice.
Nice is the most recent French resort to ban the burkini, following bans in the Corsican town of Disco, and the Riviera resorts of Cannes and Villeneuve-Loubet.
But the bans are now set to be scrutinised by France’s State Council, the country’s highest administrative court, after human rights groups challenged the ban.