Heraldo de Madrid - Australian 'pretty cooked' after smashing surfing record

The 40-year-old former surfing pro broke down in tears after beating South African Josh Elsin's previous record of 30 hours 11 minutes, braving swarms of jellyfish and pitch black seas along the way.

He briefly thanked hundreds of cheering supporters lining Sydney's Cronulla Beach during one of the short food and water breaks he was allowed, before paddling back out to try and notch up 40 hours in the water.

"I've still got a job to do. I said 40 so I'll go and give it a crack," he told reporters.

"I'm pretty cooked, yeah, but we'll push through."

Johnston was going after the record to raise more than Aus$200,000 (US$133,000) for mental health, marking 10 years since losing his father to suicide.

He was estimated to have caught more than 500 waves after starting his attempt in the early hours of Thursday morning.

Spotlights were set up to illuminate the waves at night.

His brother Ben said they had prepared for the possibility of a shark attack, but it wasn't something that had worried them.

"I surfed at two in the morning with him, and the lights actually went out so it was pitch black," he told national broadcaster ABC.

"There were a whole bunch of jellyfish out there, so it was interesting to say the least."

It is not Johnston's first time taking part in a marathon test of human endurance.

In 2020, he ran 100 kilometres along the rugged coastline south of Sydney -- covering the vast majority of the trek in his bare feet.

Y.Robles--HdM