Portuguese big wave surfer Alex Botelho has been rushed to hospital after a shocking incident at the Nazare Tow Surfing Challenge in Portugal.

Botelho, who was ranked seventh in the world last year, was being towed back to shore when the jet ski he was riding got sandwiched between two waves and was thrown high in the air.

Big wave surfers regularly use jet skis to tow them into and away from waves too large to paddle in.

Another wave then smashed into Botelho and his driver as rough conditions hindered rescue attempts and spectators looked on from the cliffs.

Footage showed Botelho being washed to shore, face-down, as rescuers raced out to drag him to safety.

Rescue crews and other surfers rush to help Alex Botelho. Photo: AAP

“Big wave surfer Alex Botelho was involved in a very serious incident during the Nazare Tow Surfing Challenge,” a statement from the World Surf League said.

“He was rushed to the hospital and we now have an update on his condition. Currently, he is stable and conscious. He will stay at the hospital for further evaluation.

“A heartfelt thank you to the safety and medical teams for their quick response. We are wishing Alex a full and speedy recovery.”

Nazare is widely acknowledged as being one of the most dangerous waves to surf in the world.

Australian surfer Ross Clarke-Jones had a lucky escape when he was washed onto rocks and was dragged underwater after coming off his board at the notorious break in 2018.

Its record-breaking waves are caused by a five kilometre-deep, 200 kilometre-wide canyon that terminates just before the town’s shoreline.

Australian surfer Mick Corbett, who competed at the event on short notice this year, said the outlook from the cliffs created an intimidating vista.

“I tell you what, it’s not when you actually go around the corner, it’s more when you look at it from the cliffs that you’re like, oh my God, because you can just see the whole arena,” Corbett told the ABC.

“But when you’re actually out there, you know it’s dangerous but you’re not really sitting on the inside, you’re sitting on the outside so you don’t really get to see the carnage on the inside that you might get to see from the cliffs.

“You see some big lines obviously come through because it is the biggest wave in the world, but I guess it’s uniform out there, not as messy as what you guys would see from the cliffs.”

With the Nazaré Tow Challenge presented by Jogos Santa Casa on Yellow Alert, let's take a look at what makes this wave so incredible. pic.twitter.com/7Z04I0UWws

— World Surf League (@wsl) February 8, 2020

The WSL estimated waves reached about 13 metres for the competition on Tuesday, as a series of storms in the North Atlantic created a big swell that, together with light winds, created “exceptional” weather conditions.

The world record for the biggest wave ever surfed is held at Nazare, where Brazilian Rodrigo Koxa rode a 24.28-metre monster in 2017.

The top 19 big wave surfers in the world, 17 men and two women, were invited by the WSL to compete in the event, where they were paired into “tow teams” to surf three, one-hour heats.

The WSL said in its promotional material that “severe wipeouts and daring feats of water rescue” would likely feature in the event.

Corbett, the only Australian participant, linked up with Spanish big wave rider Axier Muniain in the competition, which was won by Hawaii’s Kai Lenny.

Frenchwoman Justine Dupont took out the women’s prize, with the surfers voting that the Water Safety Team be awarded the “Commitment Award”.