The mum and her calf were seen at about 3pm near Tabbagai headland a popular dive site off the coast of Kurnell before continuing their migratory journey north.

Bangor resident and professional whale watcher, Wayne Reynolds, took pictures of the playful pair from Cape Solander.

Macquarie University marine mammal research group member, Maryrose Gulesserian, said the calf was a rare sight.

"It was so amazing to watch, as we don't often see such a young calf off Sydney,'' Ms Gulesserian said.

"Judging by its colour and size, I would say that it was less than a day old.

"The mum and calf were first spotted just off Tabbagai headland just before 3pm, when we watched it travel north, hugging the coast, staying close to mum,'' she said.

Ms Gulesserian is in a third season of a whale study that aims to identify and assess the potential effects commercial and recreational vessels may have on the migratory east Australian population of humpbacks.

She is doing her research from Cape Solander.

Sutherland Shire resident and keen whale watcher,

Ms Gulesserian said more than 900 whales had been spotted off Cape Solander since the end of May.

Leader online reader Graham Grocott, of Bundeena, also observed some playful whales just off the break at Garie beach on Sunday morning.

The whale watching season ends month.