Rafael Nadal
Rafael Nadal will face Diego Schwartzman of Argentina in the last-16 of the 2018 Australian Open SAEED KHAN/AFP/Getty Images

Rafael Nadal has warned that playing in severe heat can be a "little bit dangerous for health" after he eased into the last 16 of the Australian Open with an emphatic straight-sets victory over Damir Dzumhur of Bosnia on another day of sweltering conditions in Melbourne.

Though the current world number one played in mostly cooler weather in the evening as he took less than two hours to seal a comfortable 6-1, 6-3, 6-1 win, he inevitably faced questions about a heatwave that has seen temperatures reach 40C and led to criticism of the tournament's Extreme Heat Policy. The EHP was almost enforced for the first time in four years on day five and organisers say it is set to be reviewed in future.

Novak Djokovic, Gael Monfils and Petra Martic are among those to have already complained about the "brutal" conditions, while Alize Cornet said she thought playing in such high temperatures could be "very dangerous" after being seen by a doctor during her defeat to Elise Mertens.

"My opinion [is] that [it] is not safe enough sometimes, you know?" Nadal told reporters at his post-match press conference. "But [it] is not the only place. That's the real thing.

"[There] have been very, very tough conditions yesterday and today. Yeah, sometimes [it] is too much and can become [a] little bit dangerous for health. That's the real thing. It's not nice to see players suffering that much on court.

"But there is one positive thing, only one: there was no humidity, [it] was dry. That makes a big difference. Even if [it] is very warm, [it is] still very tough. But in my opinion [it] is tougher, for example, [in] Rio de Janeiro than here, because the humidity there is crazy and almost the same heat. That's the only positive thing. The rest of the things are very negative to play in these conditions."

Elsewhere on day five, Kyle Edmund - Great Britain's last remaining singles hope - fought against the heat and a two-set wobble to beat Nikoloz Basilashvili 7-6 (7-0) 3-6 4-6 6-0 7-5 in a contest that went the full distance. Andreas Seppi now lies in wait after his five-set win over big-serving Croatian Ivo Karlovic.

15-year-old Marta Kostyuk's fairytale run was ended by a swift 2-6 2-6 loss to fellow Ukrainian and women's fourth seed Elina Svitolina, while home favourite Nick Kyrgios will meet Grigor Dimitrov next after the duo overcame Jo-Wilfried Tsonga and Andrey Rublev respectively.

Marin Cilic also vanquished Ryan Harrison, Pablo Carreno Busta proved too strong for Gilles Muller and Diego Schwartzman beat Alexandr Dolgopolov to set up a meeting with Nadal.

French Open champion Jelena Ostapenko was eliminated by Anett Kontaveit, Caroline Wozniacki saw off the challenge of Kiki Bertens, Magdalena Rybarikova defeated Kateryna Bondarenko and Carla Suarez Navarro beat Kaia Kanepi of Estonia.

Meanwhile, Martic ousted determined qualifier Luksika Kumkhum and Denisa Allertova made light work of Magda Linette.