'Up to 100' people were moved on by police as they gathered to soak up the sunshine with champagne.
The group gathered in Salford Quays, Greater Manchester, with residents saying they were playing loud music and spraying champagne bottles.
Witnesses said they were dressed formally and seemed to be celebrating a special occasion.
Nearby residents claimed most of the group left after around 40 minutes but a couple remained and continued to drink and play music.
It is believed they were eventually dispersed at 2.35pm when police arrived at the scene, reports the Manchester Evening News.
Paramedic Kerry Jones said it was “upsetting” to see social distancing guidelines being ignored so blatantly.
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The 22-year-old, who lives nearby, said: “I heard a lot of noise at around 1.35pm and went outside to see a lot of people gathering on the roundabout.
“They then walked over to the waterfront and started drinking - at one point a champagne bottle was popped and then thrown into the water.
“More people kept arriving, at one point there was about 100 people there.
“They were all dressed formally, and at one point they gathered round to hold a toast to someone - I think it might have been a memorial.
“They were playing reggae on a speaker so loud it was deafening from my eighth-floor balcony.
“Lots of sports cars were there, people were revving the engines and racing up and down. After about 40 minutes most of them left, but a group of ten remained and continued to drink, play music and litter.
“They left finally at 14:35 when the police arrived - I don’t think any arrests were made.
“I’m a paramedic and I’ve seen what coronavirus does to people.
“It really upsets me to know that me and my colleagues are risking our lives while people like them are going out of their way to put themselves, their loved ones and the general public in danger.”
Another resident, who did not wish to be named, described seeing a riot van attend to break up the group.
She said: “There was at least 50 people, all drinking and celebrating, someone was spraying champagne.
“They were dresser smart like it was for a formal occasion.
“They’ve gone now, they started to disperse about 30 mins after.
“But around 10-15 stayed blasting music out and then finally a riot van turned up and they all went.”
Greater Manchester Police have been approached for comment.
