Paris police are sealing off the Seine River ahead of the Olympics opening ceremony

PARIS — A special kind of iron curtain came down across central Paris on Thursday, with the beginning of an Olympic anti-terrorism perimeter along the banks of the River Seine sealing off a kilometers-long (miles-long) area to Parisians and tourists who hadn’t applied in advance for a pass.

The words on many lips were “QR code,” the pass that granted access beyond snaking metal barriers that delineated the security zone set up to protect the Olympic Games’ opening ceremony on July 26.

“I didn’t know it started today,” said Emmanuelle Witt, a 35-year-old communications freelancer who was stopped by police near the Alma bridge while biking across town. She desperately went on her phone to fill out the online form to get her QR code, unaware that the vetting process could take several days.

Those with the precious code — either on their phones or printed out on pieces of paper — passed smoothly past police checkpoints at gaps in the barriers taller than most people.

Those without got mostly got turned away — with no amount of grumbling and cajoling making officers budge.

“That’s too much, that’s over the top, that whole thing is a pain,” grumbled Nassim Bennamou, a delivery man who was denied access to the street leading to Notre Dame Cathedral on his scooter.

“Even the GPS is confused, I have no idea how I’m going to work today,” he added.

While authorities announced the code system last year and have been meeting with local residents for months to explain the restrictions, not everyone was aware. Many visitors were redirected to reach Paris’ most iconic monuments.

“We had no idea we needed a QR code,” said Takao Sakamoto, 55, who was denied access to the Eiffel Tower near the Bir Hakeim metro station. Visiting from Japan with his wife, he took a photo of the Eiffel Tower from a distance, behind the fences and police cars. “That will do,” Sakamoto remarked with despair.

On the other hand, the fortunate visitors who entered the restricted areas were treated to the rare sight of a nearly-empty center of Paris on a bright summer day.

“It’s surreal, it really feels like we’re the only ones here,” said Sarah Bartnicka from Canada. Enjoying a morning jog with a friend, the 29-year-old took a selfie with a police officer on the deserted Iéna bridge to capture the moment.

“I understand why they’re doing this,” said Carla Money, a 64-year-old American. She managed to pass the gates with her family and was sightseeing near the Saint-Michel fountain. “I’m from

The perimeter went into effect early Thursday morning and will last through the ceremony. As an exception, Paris has decided to hold the opening ceremony on the river rather than in a stadium, like previous host cities. Most of the river security measures will be lifted after the ceremony.

Officers were under instructions to be polite and accommodating as employees on their way to work and others dealt with the perimeter for the first time.