Dozens of people queuing to get into Glastonbury Festival have been treated by ambulance crews as temperatures reached 30C (86F).
South Western Ambulance Service (SWAS) said 38 people had been treated by paramedics by 14:30 BST on Wednesday.
Thousands of people are arriving for the festival amid record temperatures and tighter security.
The gates opened at 08:00 and more than 200,000 people are expected at the event at Worthy Farm in Somerset.
People are being asked to pack light for the five-day festival and have been told to expect their belongings to be searched at the gates.
The event is being headlined by Radiohead, Foo Fighters and Ed Sheeran.
Hollywood star Johnny Depp will make an appearance, while Labour leader Jeremy Corbyn is due to give a talk and introduce US rap duo Run The Jewels.
Half an hour after the gates opened the temperature had reached 23C (73F).
It reached 30C by 14:00 and was expected to rise further during the afternoon, making it the hottest day in the event's history.
SWAS urged people to stay safe during the heatwave conditions.
"If you are heading to the Glastonbury Festival it is really important you take plenty of water with you, wear a hat and put on suncream," a spokesman said.
Festival organisers said free sun cream was available at all information points and there were water taps in most fields.
Before Wednesday, the hottest days at the festival were in 2010 and 1989, when temperatures reached 27.3C (81.1F).
In those years, revellers were left with heat stroke and exhaustion.