With the setting sun glittering on the Hudson, nearly 5,000 people turned out Monday for the fourth edition of “Dinner in White”, dressed to the nines.

In what amounts to a flashmob sunset picnic, diners get details of the event with virtually no notice, and turn up all in white — even bringing chairs.

This year, the surprise locale was Nelson Rockefeller Park, in Manhattan, with its enviable river view. As it is every year, the location was kept secret until minutes before organizers announced it.

Guests turned out with tables, chairs, tableware — all in white. The tradition dates back to an original event 26 years ago in Paris at which the organizer invited guests to all wear white so they would be easily spotted in a park.

The weather was more than cooperative. The music was more than a soupcon French, with tunes from Edith Piaf, to Michel Fugain and Joe Dassin. Guests often get a little whimsical in their dress, with massive hats, masks, feathers and the odd huge string of pearls.

This year, there was sushi, charcuterie, salads, salmon, a cheese plate and champagne before dancing. “It is a challenge to organize but it is worth it,” said a radiant Sandy Safi, co-founder of Diner en blanc international.

At midnight, the park must return to its original state. Guests even collect their own trash and cart it off.