The Reds will take on 13-time winners Real Madrid at the Stade de France, just north of the city, on Saturday, with supporters beginning to arrive on Thursday morning.
Local police were seen shutting down the Kop Bar, a Liverpool-themed pub in the city, after hundreds of football fans gathered there on Friday afternoon.
At one point officers with riot gear were seen monitoring the situation after fans spilled on to the road.
Some of those who travelled to Paris wrote on social media they had been pickpocketed, with one saying he had been threatened with a knife.
By Friday evening a sea of red shirts were seen on a grass patch covered in beer bottles close to the Eiffel Tower.
Thousands of Liverpool supporters, many ticketless, were letting off flares, chanting and drinking, with Scouse accents heard in nearby restaurants and pubs.
Beer was thrown and people were lifted above the crowd.
Up to 70,000 fans are expected to arrive, according to local authorities, with some driving for 10 hours to reach the match.
People in Liverpool shirts and holding banners and waving flags could be seen across the city.
French police have warned that wearing any football club colours is banned near the Champs Elysees.
The restriction covers the popular tourist attraction area from the Place de la Concorde to the Arc de Triomphe.
Merseyside Police’s Liverpool FC Twitter account said: “As of 15.00 on 26.05 until 18.00 on Sunday 29.05 it is prohibited to wear any football club colours in the area of the Champs Elysees.
“This includes scarves, hats, displaying banners etc. The police can issue a 135 Euro fine.”
However, supporters were still seen with Liverpool shirts and memorabilia and officers did not appear to be stopping them.
Banners seen around the city read “up the Reds” and “Conquering Europe”.
Police vans were lined up close to Gare du Nord train station where the Eurostar from London arrive, with armed officers patrolling the area.
Nicole Mannings, 52, from the Wirral, Merseyside, told the PA news agency she had been drinking from 10am.
She said: “It’s like being in Liverpool, we’re putting the Madrid fans to shame here. In terms of support there’s no contest.
“Everyone is enjoying themselves, we’re all drinking and having fun, the police have been fine really.”
Steve Ryans, 33, a fan who travelled via train on Friday morning from Kingston, south-west London, said: “No ticket but I don’t care.
“I had to see Liverpool win the Champions League in person, I missed the last few.
“There’s so many Reds here, everyone’s having a laugh. It was worth the journey.”
James Macey, 24, another supporter, from Birkenhead, said: “I left around 4am yesterday, I’m not looking forward to leaving here but I had to be here with the lads.
“I don’t even have a ticket but we’re not here for the stadium – it’s just to be with fellow Reds, it’s gonna be boss.
“Hopefully they can win to cap it all off.”
Gary Stone, 47, a landscaper from Woolton, said: “It was a real mammoth journey, 10 hours, no sleep but what a laugh it’s gonna be.
“It’ll be a carnival atmosphere – no one does it like the Reds, we’re the best fans.”
Three supporters from Cheshire said that most fans they had spoken to were in the city despite not having match tickets.
There were some reports of people losing track of their friends and family in the city.
James Hargreaves, 31, had issued a plea on social media saying his 66-year-old father was missing after drinking at a Liverpool-themed bar, but was found hours later.
Another fan said on Twitter his friend had disappeared without a phone.
#CLFINAL @ LFCHELP @SPIRITOFSHANKLY
Sorry but still NO decision made regards screening of the match in the fan zone. As soon as I have any updates on this I will let you all know. pic.twitter.com/COlR2jaKJt
— MerPol Liverpool FC (@MerPolLFC) May 27, 2022
A fan zone will be set up in the south-east on Cours de Vincennes, more than 10km away from the stadium.
Prefecture de Police, the Parisian police force, said 6,800 officers and military personnel will be “mobilised”, with flares prohibited from the fan zone.
It said up to 44,000 supporters will be permitted in the area, which will remain open from 2pm local time until the end of the match. Access will be free.