The dance music festival's site at Daresbury in Cheshire has been closed after torrential rain caused "heavy flooding".
Deadmau5, Tiesto and Groove Armada were due to play the event's last day.
Day ticket holders have been warned not to travel to the sold-out festival, while those already camping there have apparently been told to leave the site.
"No serious casualties have been reported and Cheshire Police and partner agencies are supporting event organisers in ensuring the safety and welfare of festival goers during this time," a statement read.
"All customers wishing to come to the festival today are advised that the event entrances are now closed. No entry to the festival is permitted from this point for all ticket types and ticket holders further updates will follow.
"Festival goers attempting to leave the site should follow the directions of event staff to ensure the best exit route.
"Further updates will be made available throughout the day in respect of suitable exit routes for those leaving the site and also for those travelling to the site to collect friends or family."
The festival is the latest victim of this summer's unpredictable weather, with other music events such as last month's MFest being cancelled due to extreme conditions.