Emergency services were called to Coogee Beach in Sydney's eastern suburbs shortly after 11am on Saturday, following reports a swimmer had been bitten by a shark.
Bystanders pulled her from the water and commenced first aid before emergency services arrived.
Police rendered first aid to the woman, believed to be aged in her 30s, who had suffered serious arm and leg injuries.
Ambulance paramedics then continued her treatment before police cleared nearby Coogee Oval to facilitate the landing of a Careflight rescue helicopter.
Eight ambulance crews attended the scene, a NSW Ambulance spokesperson told AAP.
The woman was airlifted to hospital.
Surf Life Saving NSW advised a shark was observed from the beach at 11.31am, according to NSW SharkSmart.
Randwick City Council has closed Coogee Beach as well as nearby Clovelly and Bronte beaches.
The most recent fatal attack in Australian waters happened on June 6, with 35‑year‑old diver Daniel Turpin bitten by a suspected 4.5‑metre shark while spearfishing with his family off Michaelmas Island near Albany.
His death followed the killing of 38‑year‑old Perth father Steven Mattaboni off Rottnest Island on May 16, and 39‑year‑old Queensland spearfisher Michael Jensz at Kennedy Shoal south of Cairns on May 24.
Both WA attacks are believed to have involved great whites, while evidence points to Mr Jensz having been taken by a bull shark.
In January, NSW made international headlines after recording four shark attacks in 48 hours.
Two resulted in people being hospitalised in critical condition, while the other two escaped without serious injuries.
The first of those maulings also occurred in Sydney's east, near Shark Beach.
A 12-year-old boy was rushed to hospital in critical condition after being rescued by mates, police said at the time.
In April, Surf Life Saving NSW announced shark bite trauma kits would be installed every surf club across the state following a wave of attacks.
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