A third woman also swept from the rock shelf is recovering in hospital.
Emergency services were called to Yena Road at Kurnell in the Sutherland Shire about 4.30pm on Monday after hearing the women had been swept into the ocean.
NSW Police Superintendent Joe McNulty said the group had been picnicking in the Botany Bay national park.
"They went for a walk to the rock shelf (where) there was a low tide at that time," he told ABC News.
"That rock shelf was very exposed and when they're exposed, they're very slippery, and they're actually quite a dangerous location to be in, especially so close to the ocean."
Supt McNulty said three of the women were knocked into the water by a large wave.
"The pressure has swept them out to sea, but luckily, very luckily, one was able to be plucked from the water by two of the group and a passer-by lended assistance as well," he said.
A nearby police helicopter spotted the women in the water and together with a police boat, rescue crews pulled two of the women unconscious from the water.
Two of the crew members commenced CPR but the women were unable to be revived.
"It's a very difficult operation doing CPR over wet people on a moving boat, or moving deck, and one of the officers drove that vessel at speed back to Kurnell," Supt McNulty said.
The women were not rock-fishing, he confirmed.Â
"They were just out there for a walk in a dangerous situation that they didn't know they were in at the time," he said.
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.
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