A Perth girl has been left with vicious teeth marks on her foot after being mauled by a shark.

Isabella Brett-Jensen was swimming in waist-deep water at North Cottesloe beach when she was mauled about 11.30 this morning.

Within seconds of entering the water, the 15-year-old felt something latch onto her foot but she couldn't see anything beneath the surface.

"I was trying to wriggle it out and then I realised there was something actually suckling on my foot," she told 9News.

Isabella Brett-Jensen was attacked while swimming at an unpatrolled beach in Perth. (9NEWS)

'Bits of my foot or like flesh actually fell off as I was walking up.' (9NEWS)

She only noticed the deep lacerations to her foot once she collapsed back on the sand.

"Bits of my foot or like flesh actually fell off as I was walking up. There was blood everywhere," Isabella said.

The young girl was swimming at an unpatrolled beach so had to phone relatives for help.

She was taken to Claremont Medical Centre where she received seven stitches in the deepest wound.

The schoolgirl needed seven stitches. (9NEWS)

A wobbegong, or Port Jackson, shark is believed to have attacked Ms Brett-Jensen. (aap)

The doctor who treated the 15-year-old believed the injuries were inflicted by a shark. (9NEWS)

Isabella said the doctor who examined her injury told her the puncture wounds may have been caused by a bite from a wobbegong shark.

The species can grow up to 3m in length and is commonly found in shallow coastal waters.

Marine experts say wobbegongs aren't normally aggressive but are capable of inflicting painful bites.

The teen said she was thankful the shark attack was only minor and has urged others to be careful.