Two Sydney beaches close after shark attacks dolphin

Two popular beaches were closed in Sydney after bull shark attacked a dolphin.

The dolphin suffered injuries to its tail and was later euthanized, Surf Life Saving New South Wales (SLSNSW), said.

Manly and Shelly beaches are well-known nature reserves where hundreds of people gather for events but, competitions that were supposed to be held on Saturday were cancelled because of the attack.

"Surf lifesavers and lifeguards cleared swimmers from the water and a large surf carnival has been suspended," the organization wrote in a statement.

Tracey Hare-Boyd, a spokeswoman from SLSNSW said that, luckily, no person had been injured or involved in the attack.

SLSNSW said it was monitoring the shark activity via a drone and urged people not to enter the water until it was deemed safe by lifeguards.

An eyewitness who was on Shelly beach told ABC News she was initially delighted to see a dolphin swimming in the bay.

But she soon learned there was a shark in the water and swimmers were told to stay on dry land.

"We came back and saw the dolphin was on the beach which was really incredibly sad," she said.

Beaches from Shelly Beach to Queenscliff Beach remain closed and people have been urged to be vigilant and follow shark safety advice.