The men's Tre Valli Varesine race was suspended and then stopped with 110km to race due to torrential rain and an increased risk of crashing.
The race started as planned with a reduced distance of 170 km but the rain continued to fall heavily, with water running onto the road at some points and drains overflowing.
The riders, including world champion Tadej Pogačar (UAE Team Emirates) stopped in the finish area in the centre of Varese to speak to race organisers after three laps and then the race was abandoned. Teams confirmed the news via social media, posting images and videos of the extreme weather conditions.
Before the race was stopped, Enric Mas (Movistar), Georg Steinhauser (EF Education-EasyPost), Felix Engelhardt (Jayco–AlUla), Lorenzo Germani (Groupama-FDJ), Romain Bardet (Team dsm-firmenich PostNL) and Tobias Foss (Ineos Grenadiers) staged an early attack as they looked to stay warm and safe on the roads around Varese.
The peloton was timed at 4:00 but then, after some initial discussions out on the course with the race organisers and UCI commissaire, the riders stopped on the finish line in Varese.
Pogačar spoke to other riders and the race director about the worsening conditions and then stood on the front line of the riders when they stopped in central Varese.
"We tried to race and did a good race until we could. Then on the last lap, on the downhill, I was in second position behind [Alessandro] Covi and we couldn't see where we were going," Pogačar said before going to his UAE Team Emirates bus for a warm shower.
"Everybody wanted to stop. It was just a matter of time about when some guy would crash. When there's standing water, it's not good.
"We understand the organisers - that they want to race - but in the end the riders made the right decision not to. We are sad for the race to not continue, but it's like this. We talked with the organisers, luckily everybody was reasonable.
"I could see how heavy it was for the boss of the organisation. There were tears in his eyes. This race means a lot to them and it's a beautiful race, but when you can't race you can't. They understood that immediately. I'm really thankful for that and happy that they decided to end the race."
Pogačar appeared especially concerned about crashes in deep water.
"Those are the worst crashes, when you lose the handlebars and go over the bike," he said.
"It's not like when you slide on the asphalt and just get a few scratches if you're lucky," Pogačar continued If you crash when you don't expect it and go over the handlebars with your head, we know how it is with concussion. I know a lot of friends from the peloton who had concussions this year. It's something we need to be more careful about in the peloton."
Race organiser Renzo Oldani spoke briefly and accepted that safety comes first.
"It was a difficult decision. Safety comes first, for the riders and for the spectators," Oldani said.
"This hurts after a year of hard work but I'll try to encourage my staff and volunteers after the riders promised to be back next year."