The archbishop of Paris re-opened Notre Dame cathedral on Saturday by symbolically knocking on the doors and entering the 12th-century landmark which has been restored after a devastating fire in 2019.

Wearing new designer vestments and carrying a staff cut from one of the roof beams that survived the inferno, Laurent Ulrich joined hundreds of VIPs inside the Gothic masterpiece for a two-hour ceremony.

Ulrich commanded the cathedral to "open your doors" and he entered the magnificently-restored edifice.

US President-elect Donald Trump sat on the front row as guest of honour next to French President Emmanuel Macron, with invitees marvelling at the freshly cleaned walls, new furniture and state-of-the-art lightening installed as part of the cathedral's overhaul.

Other dignitaries in attendance included outgoing US first lady Jill Biden and Prince William.

Outside, small crowds of Parisians and tourists braved wet weather and high winds to witness the renaissance of a beloved monument which came close to being totally destroyed by the inferno that toppled its roof and spire.

The reconstruction effort has cost around US$750 million, financed from donations, with the re-opening achieved within a five-year deadline set by Macron despite predictions it could take decades.

Workers had to overcome problems with lead pollution, the Covid-19 epidemic, and the army general overseeing the project falling to his death while hiking in the Pyrenees last year.

It is "a cathedral like we have never seen before," Philippe Jost, who took over as project manager last year, told Franceinfo radio, adding that he was proud to "show the whole world" a "great collective success and a source of pride for all of France".

Saturday's service featured prayer, organ music and hymns from the cathedral's choir.

A public concert planned in front of the cathedral featuring Chinese piano virtuoso Lang Lang and possibly US singer and fashion designer Pharrell Williams had to be pre-recorded on Friday night because of the stormy weather. (AFP)