Mick Fanning was shaken to the core after his infamous encounter with a shark off the South African coast.

Now, the Australian surfer has been rattled once again by the sight of a fin during his return to the water in northern NSW.

In a clip released by Channel Nine to promote its upcoming interview with Fanning, the 34-year-old is filmed jumping on to a jet-ski and returning to the beach to tell reporter Peter Stefanovic that he saw a fin.

"There was a fin, there he is," he says, pointing out to the surf at Hastings Point on the Tweed Coast.

"Straight out. I just saw it."

The television crew were filming Fanning's return to the water on Saturday following the incident at Jeffreys Bay, during which he fought off a shark during the final round of the J-Bay Open world surfing competition.

Fanning posted a photo on Instagram on Saturday to mark his first surf back, saying it felt "so good".

It came on the same day as the birthday of the late world champion surfer Andy Irons, who died in 2010.

"Surfed by myself but had Andy in my thoughts. Happy Birthday brother," he posted.

Fanning told Stefanovic it was "hugely important" for him to get back in the water although he appeared nervous as he pulled on his wetsuit for the first time.

The promotional clip doesn't say if the fin belonged to a shark or a less menacing creature.

A surfer in his 40s was attacked by a great white shark at Evans Head on the northern NSW coast on Friday morning, while several beaches around Ballina have been closed recently because of shark sightings.

Four beaches were closed on Sunday after a 3½ metre-long shark was spotted off the coast.

Fanning has announced he will resume competition next month at the next World Surf League event, the Billabong Pro in Tahiti.