"If we sweat, we sweat -- we know each other well," laughed Cathy Butcher, 73, arriving with her daughter Helen.

The retiree said she had a "dodgy hip and my daughter is heavily pregnant" but that they would focus on keeping cool and enjoying the day.

"We're hoping for a cool breeze" and some "great tennis", added her 31-year-old daughter.

It was provisionally the hottest start to Wimbledon on record, according to the Met Office.

The BBC said temperatures at the All England Club had topped 32 degrees Celsius (89.6 Fahrenheit) by mid-afternoon.

The previous record was set on June 25, 2001, when the mercury tipped 29.3C.

Parts of the UK are currently in the grip of a second heatwave in a month, according to weather experts, with the sweltering temperatures expected to reach 34C in London and southeast England Monday.

London start-up boss Sean Tipper said he had made sure to come prepared after failing to heed warnings before.

"Wimbledon when it's really hot is quite sweaty," he told AFP on a family day out with his wife, mother and aunt.

The 31-year-old said they had brought hats and sunglasses plus "a mini-fan and good hope".

"Last time we were very hot so this time we've got rosé (wine) in a cooler so we can do a better job," he joked.

The hottest June day ever recorded in the UK was 35.6C on June 28, 1976.

But Wimbledon is more used to making headlines for the rain than the heat.

- Cooling scarves -

Tournament chief executive Sally Bolton said they were "absolutely ready for it and actually delighted that it's sunny and not wet like it was last year".

For Chilean tennis fan Maria Verdugo, 40, there were pros and cons to enjoying tennis in different weather conditions.

"On balance, though, I prefer the sun, it's more exciting," she said, clutching a glass of Pimm's with plenty of ice.

Under a heat rule to protect players' health, officials will be taking heat stress monitor readings 30 minutes before the start of play and then at 2:00 pm (1300 GMT) and 5:00 pm.

The rule allows a 10-minute break to be taken at certain points in a match when the heat stress index is at or above 30.1C.

Protocols are also in place to look after ball-boys and ball-girls on court who have access to cooling scarves.

Some visitors admitted they were wilting in the heat.

"It's horrible, unbearable," said retiree Linden Barnett after an hour watching Italy's Fabio Fognini play Spain's Carlos Alcaraz on centre court.

"You can't sit in it, we have to keep coming out to cool down," she said, adding that the players "must be feeling it".

"I need a long cold drink, preferably with gin in it, at least then I'd forget how uncomfortable I am," added youth worker Mel Megson, shielding herself from the relentless sunshine under some shrubbery.

"Some rain would be good -- you'd find me dancing in it," she added.

Despite the scorching heat, hundreds of hardy tennis fans without pre-booked tickets stuck it out in the queue to get in all day.

"We've been waiting since 9:00 am just with a bit of shade and somesun screen," said Sharon Rivera, 48, from Puerto Rico at around 6:00 pm.

"It's been too much, but I'm relieved to finally be near to the end of the line," she said.