Hawaiian big-wave surfer Garrett McNamara may have broken his own world record by riding a wave that topped out at a massive 100 feet off the coast of Portugal.

McNamara set the previous record when he surfed a 78-foot wave at the 2011 Billabong XXL Global Big Wave Awards in Nazare, Portugal, after being towed into the swell by Jet Ski.

A 100-foot wave is equal in height to a 10-storey, or 30-metre-tall building.

At this year's event, it appears McNamara may have beaten his old Guinness World Record by more than 20 feet -- though Guinness has not yet confirmed the feat.

In a teaser video released by organizers of the contest, McNamara appears to be seen in a brief clip coming down the face of a massive wave -- said to be the 100-foot record-breaker.

And SurferToday.com suggested McNamara may have beaten his old record after surf photographer To Mane published a "breathtaking" photo of McNamara charging down the face of "what seems to be a 100-foot wave" on Jan. 28.

McNamara also posted the photo to his Facebook page, though he has not yet confirmed he has a new record under his belt.

On his Twitter feed, McNamara appeared jubilant, however, saying "Oh how I love Nazare," and thanking his supporters. But he didn't offer specific details.

"Today was an awesome day and so fun to be out there," tweeted McNamara, who lived in Pittsfield, Mass. before moving to Hawaii when he was 11.

The Nazare wave is reportedly generated by a 300-metre deep underwater canyon, which is roughly five kilometres wide where it begins at sea, but narrows dramatically as it approaches shore.

The underwater trench acts as a funnel, forcing more and more water into the wave as it approaches land, and creating massive swells before the wave finally breaks into 100-metre high cliffs.

"You can't contemplate coming off because it would kill you," McNamara told The Observer in 2011 after setting his original record.

While McNamara's original record-setting ride was reported to have occurred on a 90-foot wave, Guinness later revised the wave's height to 78 feet.