Warren Gatland has no doubt Wales are fully conditioned for Bordeaux's blistering heat as they aim to turn up the temperature on Rugby World Cup opponents Fiji.

It is due to hit 36 degrees Celsius on Saturday, while not dropping much below 30 a day later despite a kick-off of 9pm local time on Sunday (Monday AEST) in a match which will be absolutely key in a group which also features Australia.

Wales, though, feel they could reap the benefits of punishing conditions at training camps in Switzerland and Turkey that formed a central part of their tournament warm-up.

"I think in international rugby you have to go to dark places and you have to be hurting," Wales head coach Gatland said.

"It's whether other teams are hurting that little bit more than you.

"Everyone is talking about the heat being an advantage to Fiji, but we've had some pretty gruelling sessions in heat so we are conditioned to that.

"We've been comfortable with the pace of the game and the intensity of the game."

Wales meet Fiji for the fifth successive World Cup in a pool game, and while they have won three in a row after being dumped out of the 2007 tournament, they are expecting a fierce challenge.

Fiji's quality - and a far stronger set-piece than previously - was highlighted in their historic victory over England at Twickenham last month.

Gatland added: "You've just got to defend well for a start. We know they are dangerous.

"At some stage, they will make a break or get an offload away. It's then how we react to that quickly.

"For us, we've spoken about discipline and keeping them out of our 22. They tend to come alive in opposition 22s. We are in a good place for the challenge, physically and mentally."

It will be Gatland's fourth World Cup at the Wales helm after masterminding semi-final appearances in 2011 and 2019, while they also reached the quarter-finals in 2013.

There are similarities with that 2011 campaign in New Zealand, when Wales were captained by a 22-year-old Sam Warburton, while this time around 23-year-old Jac Morgan leads them into tournament battle.

"We've had some new faces come in, which has been great for the group. A lot of young players have got some experience," Gatland said.

"We've had some issues in Welsh rugby. Hopefully those are behind us now and we can completely focus on this World Cup."