The body of a diver has been retrieved from rocks on Victoria’s Mornington Peninsula, bringing to four the number of drownings across Australia since Christmas Eve.

The man was diving with a friend off the coast near Cape Schanck when he got into difficulties shortly after 6.30pm on Christmas Day, Victoria police said.

His body was later retrieved by an emergency helicopter crew.

On Monday a father and son drowned at a beach on Phillip Island in Victoria and the body of a Korean man was recovered at Lake Conjola on the New South Wales south coast after going missing while snorkelling on Christmas Day.

A fifth man was in a serious but stable condition after being pulled unconscious from a swimming pool in regional NSW.

The 51-year-old man was found floating face down in the pool in Scone in the NSW Hunter region on Christmas Day, a NSW Ambulance spokesman said.

The man had been in the pool for up to two minutes and was resuscitated at the scene before being flown to John Hunter hospital by the Westpac Rescue helicopter.

He was placed in a medically induced coma for the flight, according to a rescue helicopter spokesman.

The first drownings occurred on Christmas Eve on Phillip Island, when emergency services were called to The Colonnades at 5.30pm after three men were reported to be in distress, Victoria police said.

A 45-year-old man and his 20-year-old son – both from Cranbourne East in Melbourne – died at the scene.

A young boy who was swimming with them survived, but a police spokesman could not confirm on Tuesday afternoon if he was also related.

“A 45-year-old man was pulled from the water however could not be revived and was declared deceased at the scene,” Victoria police said. “A second man, aged 20, was also pulled from the water and died at the scene.”

Ambulance Victoria confirmed that the young boy was taken by ambulance to Monash medical centre in a stable condition.

Police said they would prepare a report for the coroner.

NSW police said a 46-year-old South Korean national’s body was pulled from the water at Lake Conjola before 3pm on Tuesday by his family and bystanders, who had been searching for him.

Lake Conjola on the south coast of New South Wales. Photograph: Genevieve Vallee/Alamy Stock Photo

Police said efforts were made to revive the man, who was in Australia on a tourist visa, but he was declared dead at the scene.

Four people drowned in two incidents last week at Moonee beach near Coffs Harbour on the NSW mid-north coast.

Victoria’s premier, Daniel Andrews, urged Victorians to avoid risks and swim only in supervised areas.

“Don’t have what should be such a special time for you and your family turn into a tragedy,” he said on Wednesday.

“Be aware of the circumstances, don’t drink and swim and if you are not confident in your swimming ability, then the only place you can swim is at a supervised beach.”