People travelling to Glastonbury by car, caravan or campervan have been warned not to travel because " wet weather and ground conditions" are causing congestion.

Festival organisers urged people who had set off but not yet reached the site to "stop somewhere safe and warm".

"If you are already queueing to get into the site, please bear with us and follow the instructions from the signage and traffic managers," they advised in a Twitter message.

People arriving by coach or train were told to travel as planned but to be prepared for " your journey to take longer than usual".

Wednesday will see the start of arrivals at the event, with more than 180,000 festival- goers expected to pour in over the rest of the week.

The Met Office posted a weather update on its Twitter account, saying: " Further outbreaks of #rain over #Glastonbury this morning, adding to the already very wet ground conditions."

The festival site was dubbed a mudbath earlier in the week following showers, and pictures shared by workers at the festival showed boggy fields and submerged paths.

This year's headline acts are Muse, Adele and Coldplay, who will all take to the famous Pyramid Stage.

Wiltshire Police warned people travelling by road to seek an alternative route following a four-car accident on the A303 westbound which has brought traffic to a standstill.

"No serious injuries. Road blocked, seek alternate route," they tweeted.

Avon and Somerset Police echoed the warning from festival organisers.

A force spokesman said: "We're strongly advising people to avoid travelling on main roads leading to the Glastonbury Festival site in Pilton due to heavy traffic.

"At the moment, traffic is queuing from the festival site in Pilton along the A361 to West Pennard.

"There's also very heavy traffic on the A37 north and south of the junctions with the A361. The traffic is congested south of the A361 to within a few miles of the A303.

"We're advising people to avoid travelling in this area unless it's absolutely necessary. If you're planning to travel to the festival, please delay your journey until later in the day or avoid coming to the site today altogether.

"If you've already left, then find somewhere to stop and wait until the traffic congestion situation improves.

"A temporary campervan and caravan holding site has been set up at the Bath & West Showground.

"We'd also ask people to stay in their cars if possible, so when traffic starts moving it doesn't cause further delays."

AA president Edmund King also warned of "heavy and widespread congestion" on the roads around the festival site, including severe delays on the A361, A37 and A39.

"We would advise festival-goers not yet on the approaches to Glastonbury to travel later," he said.