French security forces began locking down large parts of central Paris on Thursday ahead of the hugely complex Olympics opening ceremony next week on the river Seine.

The opening parade along six kilometres (four miles) of the river led to the closure of riverside central districts to most vehicles from 5:00 am (0300 GMT) on Thursday.

Anyone wanting to enter the highest-security "grey zone" along both banks of the Seine, such as residents or tourists with hotel reservations in the area, will need a security pass in the form of a QR code.

The City of Light is transforming ahead of the July 26-August 11 Olympics when around 10 million spectators are expected

Temporary sports stadiums have sprung up at popular locations such as the Eiffel Tower, the Invalides or the Place de la Concorde, while new Olympic VIP lanes are the latest traffic-snarling addition.

"It's true that our concept of having a large number of temporary sites in the heart of the city, obviously with that, there are constraints, but I feel like people are seeing what we're doing," Paris 2024 director general Etienne Thobois told AFP last month.

Many central Metro stations will also be closed on Thursday until the day after the opening ceremony, which will see 6,000-7,000 athletes sail down the Seine on around a hundred barges and river boats.

It will be the first time a Summer Olympics has opened outside the main athletics stadium, with up to 500,000 people set to watch in person from stands, on the river banks and from the overlooking apartments.