Heavy rain in Byron Bay on NSW's North Coast, had already forced campers to sleep in their cars, while others were forced to wait outside for up to 12 hours to enter festival grounds.

Organisers had pledged the festival would go ahead on its first day, Friday, July 22, but just after midday all performances on the main stages were cancelled "in the interest of patron safety".

"In consultation with all relevant emergency services, we have decided to err on the side of caution and cancel performances on the main stages today [Friday] only," organisers said in a statement.

"Day patrons are asked not to attend to the festival today while we work on repairs.

"Our event team is working very hard to provide the best experience possible under the current circumstances.

"We look forward to Saturday and Sunday programming moving ahead as planned."

Earlier, festival goers had slammed organisers for the long wait to get into the grounds for the annual event.

"Five hours waiting in line. No toilets. No spots left in family campground. No one knows whats going on. Stuck in a car with a nine-year-old and you only make communication now?! People have been waiting since 2pm," Geo Jazmin posted to social media.

Keira Tomlin posted that she had been in the line so long that her car was about to run out of petrol.

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Noah Dixon wrote "I've been in the line over six hours and still haven't gotten [sic] a campsite".

Local resident Hannah Lange lashed out at organisers for the huge backlog of cars that were clogging roads.

"Two hours of navigating traffic dodgey [sic] back roads in the rain with my two little kids in the car trying to get home from school, which is usually a 10 min drive. Now I have to keep them home today which impacts my work and us financially," she posted to the festival's Facebook page.

"After what we've all been through with floods, there should have been better consideration to us all.

"Don't get me wrong I love festivals and I love Splendour, But this is just so inconsiderate and dangerous. Reduce capacity, change locations or pay and work with council for better road access to parklands."

Sarah Cahill called for the festival to be relocated permanently.

"The Byron and Mullum [Mullumbimby] shire don't have the capacity for this event anymore," she said.

"It's one thing for people to be lined up to get to your overcrowded bender, but it's another to have locals and emergency services stuck in traffic for hours on end for a festival they aren't even going to. Had how long to figure this out? Money grabbing at its finest."