A 13-year-old girl who was bitten on the calf and foot by a shark on the central coast of New South Wales says she "dropped in" on the animal while surfing.

Promising junior surfer Kirra-Belle Olsson was at a break at Avoca Beach at about 6.30am AEDT when she took off on a wave and landed on top of the one-metre shark, which then bit her.

Kirra-Belle and her father Jamie, both keen surfers, were in good spirits as she was treated in Gosford Hospital.

In surfing terms, a "drop in" means taking a wave that should be ridden by another board rider who has priority, and it is a major insult.

"I took the wave and then I twice felt something grab my foot, and I thought it was a mate behind me trying to scare me," Kirra-Belle said.

"Then the third time it (the shark) swung me around and tried to pull me under," she said.

"I saw the tail and I was just like, 'whoa', and I didn't know what to do, so I just started screaming," she said.

"I paddled in and I was in shock and just started laughing.

"I thought 'whoa', what the hell. I just got bitten by a shark, oh my god."

Kirra-Belle said despite the nature of the attack, she did not really feel much pain from the shark bites.

This photo captures the moment Kirra-Belle Olsson is carried from the surf after the shark attack at Avoca Beach. ( Seven News )

"I think my wetsuit stopped it (the bite) from going through to my bone," she said.

"I didn't really see it. I just saw the tail pop up behind me while it was on my leg.

"I was thinking has it taken my whole foot off, but it didn't feel that painful.

"Then, when I was paddling in I was looking at my foot and it was all floppy, and I was like 'oh my gosh, no' - but it was fine, I just had a few gashes.

"I just started screaming because I didn't really know what to do."

Kirra-Belle was treated for deep lacerations to her lower leg and she will undergo surgery later today.

After the attack, Kirra-Belle made her way back to shore and she was treated at the scene by bystanders, who then drove her to hospital.

'It's more than a couple of stitches'

Her dad, Jamie, said she was lucky not to receive far more serious injuries.

"She landed on top of the shark, and part of her leg was presented to the shark like a fish, and it latched on for a little bit," Mr Olsson said.

"She just thought it was a mate mucking around with her and pulling her down.

"She (rang me) in the confusion and said 'Dad, I'm fine', and she was laughing about it," Mr Olsson said.

"I was like, 'phew', but she could have been missing half a leg."

Kirra-Belle's mother, Kyla, also said she was pretty relaxed about the attack, despite the deep cuts to her leg.

"She was like, 'Mum, I'm fine, it's just a couple of stitches'. Then I saw the photo and it's a bit more than a couple of stitches."

Gosford City Council closed Avoca Beach and North Avoca Beach today and lifeguards will monitor the area for sharks throughout the day.

Lifeguards are patrolling the beach on jet skis and have told people not to enter the water. There has been no sign of the shark.

Avoca Beach is a popular holiday destination with a reputation for being prone to shark encounters.

In 2012, a local 28-year-old man was attacked by a shark at North Avoca Beach. The man reported feeling his hand pulled under his board while he was in shallow surf at sunset.

He was treated for a small puncture wound to his forearm and wrist.

At the time local lifeguards speculated the shark was probably a bronze whaler.