Two women who were “sightseeing” at a notorious coastal black spot are dead after they were swept off rocks in Sydney’s south on Monday afternoon.

Police said a group of five people were walking along a rock platform in Botany Bay National Park when they were struck by a large wave about 4.30pm.

The powerful wave “pushed” three women into the dangerous water at Kurnell where they struggled.

One of the women was able to be recovered with the help of two males from their group and a bystander, Superintendent Joe McNulty told Sunrise.

“The other two females drifted out to sea,” he said.

“A short time later a police helicopter was in the vicinity and flew over and spotted the females.”

Botany Bay Water Police recovered the two women and immediately began resuscitation efforts.

“It is a very difficult task on a moving police vessel, taking into account it is wet, slippery and defibs (defibrillators) in those situations are very difficult to get a good connection,” he said.

“That police vessel sped into Botany Bay to the Kurnell side, was met by Sutherland police, a waiting ambulance, helicopter and quick medevac from the vessel on to the shore, where they continued to be worked on.”

McNulty said the group of five had been picnicking at Botany Bay National Park, in an area also popular with whale watchers.

Police have started an investigation into the incident but have not found any suspicious circumstances.

It is the second drowning incident at Kurnell in less than a fortnight.

Two fishermen were swept off rocks on Cape Solander Drive on May 28, in an area declared a high-risk rock-fishing location where anglers must wear life jackets.

The deceased women are yet to be formally identified.