Glastonbury organisers have urged people planning to arrive by car or campervan to stay away until queues at the site are cleared.
Some people have been stuck in queues around the site throughout the night, with one calling the organisation "shambolic".
A statement posted on the festival's Twitter feed on Wednesday morning said: "If you are coming to the festival by car or campervan, and have yet to begin your journey, please do not set off."
It said wet weather and ground conditions are causing "heavy traffic congestion" around the festival site in Somerset.
The statement urged anyone who has already set off to "stop somewhere safe and warm".
One person responded: "Bad planning and management are causing heavy traffic congestion - not rain!"
Another said: "This post should have been put up hours ago."
One said: "Journey is now into 24 hours, worst festival experience after 15 years. Shambolic."
Those who are travelling to the festival by coach or train are asked to set off as planned but be prepared for their journey to take longer than usual.
The statement added: "If you are already on the site, gates will open as planned. But, as always, there is no entertainment today. The festival's entertainment does not begin until Friday."
Those travelling to Glastonbury are asked to keep checking the official Twitter feed @GlastoFest, or tune into Worthy FM on 87.7FM.
The Glastonbury Festival website has been replaced with a temporary holding page "due to high traffic".
Despite recent rainfall, the weather forecast for the next few days is generally good.