Large parts of the Danish capital were shut down for the first stage of the race, with a rain shower making sections of the 13-kilometer (eight-mile) route potentially treacherous for the cyclists — especially the stretch across the square of Amalienborg Palace, the main residence of Denmark's royal family, which is paved with cobble stones.
Swiss rider Stefan Bissegger became the first one to crash on the slippery roads, going down twice, but was quickly back on his bike.
The time trial, a race against the clock that sees the riders set out one by one in intervals, will also go past some of Copenhagen's other best-known landmarks, including the Little Mermaid statue, sitting on her perch at the entrance of the harbor.
The rain had stopped by the time the race started but the roads were still soaking wet.
Among the thousands of fans, some waving the red-and-white Danish flag, was the country's Prime Minister Mette Frederiksen.
“It is wonderful to see,” Frederiksen said.
“I grew up with my dad being glued to the television screen to watch Tour de France.”
It's the first time the classic race starts in Denmark.
Earlier Friday, Denmark's Crown Prince Frederik went for a ride along the route.
“I have just ridden the route by bike. It is great to see the great support for the tour at home,” said the 54-year Frederik, sporting a helmet, shorts and a t-shirt.
The palace also published on Instagram vintage photos of Danish royals riding bicycles, including Frederik's great grandfather, King Christian X and the current Queen Margrethe.
Some locals got up early to get a good spot along the route, including 77-year-old Grethe Dalsgård, who told Danish broadcaster DR that she arrived at around 7:30 a.m. and was standing some 20 meters from the finishing line by the City Hall.
"I am sure I will be able to see them all,” Dalsgård told DR.
The three-week race has two more stages in Denmark this weekend, including crossing the Great Belt Bridge that links the Zealand island, where Copenhagen sits and the central isle of Funen.
The start in Denmark — the 24th time that the race has started outside of France — was supposed to be held in 2021 but was postponed a year because of the coronavirus pandemic.
After the Danish stages, the riders travel to France with a stage between Dunkerque and Calais.
Last year, Slovenian rider Tadej Pogacar won the Tour for the third straight time and he is a firm favorite to defend his title. The race ends in Paris on July 24.