A woman and a man have died and two people are missing following three separate incidents on Sydney waters in the past 24 hours, with multiple beaches across the city now closed.

Emergency services were called to Maroubra Beach in Sydney's eastern suburbs about 4am on Thursday following reports a person had been swept out into the ocean.

Two people have died and others are missing following incidents across the Sydney coastline on New Year's Day. (ABC News)

Authorities were told a 25-year-old woman had been hit by a wave and knocked into a tidal pool, before swells carried her further into the ocean.

A multi-agency search located the woman, believed to be a Chinese national, about an hour later but she could not be revived.

The woman was swept off the rocks at Maroubra and could not be revived. (ABC News)

Meanwhile, a search is underway for a swimmer believed to be missing at Coogee Beach.

The alarm was raised at 6am when a man believed to be in his 20s got into trouble in the water.

He was with two other men, who were rescued by off-duty surf lifesavers.

A police officer also entered the surf to assist with rescue efforts.

The third man went underwater and is yet to be located. Surf Life Saving NSW personnel and emergency services remain at the scene.

Coogee Beach is one of a number of beaches that will be closed on New Year's Day. (ABC News)

Large waves, a 3-metre swell and squally conditions are hampering the search effort.

Surf Life Saving NSW chief executive Stephen Pearce said the tragedies marked a "terrible" start to the new year.

"We knew that New Year's Day was going to be very busy operationally for us because, statistically, we see that people are three times more likely to drown in that period rather than any other time during the year," he said.

"Already we have seen tragedies unfold that will ripple across so many families and so many first responders."

Teenage boy missing, beaches closed

A search is also due to resume for a 14-year-old boy who has been missing since the boat he was in capsized at the northern end of Palm Beach on New Year's Eve.

A boat capsized off Palm Beach, on Sydney's northern beaches, on New Year's Eve. (ABC News)

One man climbed onto rocks at Barrenjoey Headland and was winched to safety by emergency services before being taken to hospital with serious injuries.

Another man pulled from the water could not be revived and died at the scene.

It comes as multiple beaches in Sydney were shut off to swimmers due to hazardous conditions.

They include Coogee, Bronte, Clovelly and Tamarama beaches in the eastern suburbs and Long Reef, Collaroy, Narrabeen and Palm beaches in the northern beaches.

As of lunchtime on Thursday, Surf Life Saving Australia's Beachsafe website had over two dozen swimming spots listed as closed.

Large swells are hampering search operations at Coogee Beach. (ABC News: Danuta Kozaki)

Volume of drownings unexpected

Surf Life Saving NSW conducted 19 coastal rescues on Wednesday, said Mr Pearce.

"[They were] predominantly groups of children, and fortunately they were rescued either by lifesavers or lifeguards," he said.

"Last night at 6:50pm, off-duty lifesavers again rescued a 50-year-old male that was unconscious … and retrieved him and brought him to shore and commenced CPR until the ambulance arrived and he was airlifted to hospital in a critical condition."

There have been 24 coastal drowning deaths in NSW since July, up from 19 in the same six-month period last year.

Mr Pearce said there had been 85 rescues in the week since Christmas Day alone.

People are being urged to avoid the Sydney coastline. (ABC News)

"This spate of rescues at the moment and drownings have just caught everyone off-guard over this new year's period," he said.

"The efforts of lifeguards and the efforts of volunteer life savers have dramatically saved so many people in this 72-hour period."

'Incredibly unpredictable' conditions

Officials have urged people to steer clear of the coast.

"Don't head down onto any rocky headlands or rock ledges because this is a period of time where we do see people swept into the ocean because of these swells," Mr Pearce said.

Coogee resident Anna said she has never seen such poor conditions at Coogee Beach. (ABC News)

Coogee resident Anna said she had never seen the beach "quite this rough".

"I swim each day, I was with mates and freak waves were coming and washing our clothes away … which has never happened," she said.

"The usually quiet pools were getting shut because the dangerous conditions were just too risky for people, even incredibly confident swimmers.

"The swell is huge and super choppy, incredibly unpredictable."