Four shark attacks in three days have sent shockwaves through beach communities as new warnings on shark safety are issued.
A 39-year-old man was taken to hospital after being bitten in the chest at Point Plomer, north of Port Macquarie on the NSW mid-north coast, on Tuesday morning.
It was the fourth attack on the state's coastlines since Sunday, leading to a swathe of beaches being closed.
Two people - one a boy - have been left with serious injuries after shark bites in two Sydney incidents, while a second boy's surfboard had chunks bitten out of it.
James Cook University marine biologist Jodie Rummer said a combination of very warm water, active weather systems and recent heavy rainfall along the NSW coast had likely drawn sharks to food plumes near rivers and stormwater drains.
"We also have more people in the water than ever before, which naturally increases the chance of encounters," she said.
The key was being shark smart, including avoiding turbid waters after storms and following local advice and beach closures.
"Sharks are a sign of a functioning ocean, not a broken one," she said.
University of Sydney's Chris Pepin-Neff, who has written a book on shark policy, suggested Sydney Harbour's 100-year-old sewage pipes were also likely to blame.
The pipes overflow with just 20mm of rain. More than 120mm fell on Sunday.
He said the spike in attacks shows "there's a unique environmental condition that is more than just the heavy rain."
Surf Life Saving NSW chief executive Steven Pearce said "turbid and brackish" water created prime conditions for bull shark activity.
State officials are working to identify the species of shark involved in each incident.
Premier Chris Minns said he was open to a more robust system of warnings for swimmers and surfers.
"Our warning system and communication needs to be beefed up, particularly during stormy weather," he told 2GB radio on Tuesday.
Some 20 beaches were closed on Tuesday, including along the 30km coastline marking Sydney's northern beaches, as well as at surfing hotspot Crescent Head, near the site of Tuesday's mid-north coast incident.
That victim was discharged from hospital later in the day, telling authorities that a shark took hold of his surfboard in the incident.
Paramedics earlier revealed a Formula One-style pit stop to deliver extra blood might have saved the life of a man mauled in Sydney's north on Monday evening.
The man, aged in his 20s, was bitten at Manly's North Steyne Beach and underwent surgery for severe lower-leg injuries.
He remains in Royal North Shore Hospital in a critical condition after requiring 13 units of blood at the beach and during the drive to hospital.
Such was the extent of the man's blood loss, highway police met treating paramedics en route to drop extra supplies.
"They said it was almost like an Formula One pit stop of 10 seconds or less where they just opened the door, blood went in and then they continued on," NSW Ambulance acting superintendent Christie Marks said.
"This is something that doesn't happen a lot ... that is going to give him the best chance of surviving."
On Sunday, a 12-year-old boy was attacked while swimming in Vaucluse in Sydney's east, requiring surgery for severe injuries to both legs.
An 11-year-old boy narrowly avoided injury at Dee Why, with a shark taking a chunk out of his surfboard on Monday morning.
More than 30 SMART drumlines have been deployed along Sydney beaches, while shark listening stations and aerial surveillance have been ramped up.
