A man has died after his newly-bought yacht capsized off Sydney’s south on Monday morning.

A woman who swam to shore from the vessel at Boat Harbour near Kurnell, about 30 kilometres south of the Sydney CBD, alerted authorities to the incident about 5am on Monday.

Rescuers then spotted the man’s body floating in the water at about 5.50am near Wanda Beach, near Cronulla.

The man, who the ABC believes was in Sydney to sail his boat to his hometown in Queensland, was unable to be resuscitated by rescue authorities after being pulled to shore, police say.

“Inquiries are continuing in relation to what actually has occurred, however, the seas were quite hazardous … which obviously made it difficult for rescuers,” Acting Inspector Mel Thompson said,

The woman was taken to Sutherland Hospital for observation after being treated for hypothermia at the scene.

“It’s a tragic circumstance for that time of the morning and the fact it was still quite dark it is remarkable she got to the shore,” NSW Police Acting Inspector Melissa Thompson told Channel 9.

“The seas were quite hazardous which would have made it difficult for rescue efforts,” Inspector Thompson said.

The yacht, named C.C. Rider, has not yet been removed from the shore due to the hazardous weather conditions.

Local Sutherland police and the Marine Area Command are investigating the incident.

-with AAP