A SOUTHERN right whale calf, almost certainly born in Sydney Harbour a few days ago, was spotted travelling north at a serene pace, by its mother's side, off Barrenjoey Head last night.
The pair were seen just after dawn, just off Balmoral Beach, before moving through the heads in late morning and ''playing really, really gently'' just off Manly's Fairy Bower at lunchtime.
The presence of a newborn southern right whale in the harbour is extremely rare, and the event was made all the more unusual by the arrival of a second mother and child pair just off Botany Bay late yesterday.
The first pair may return to Sydney Harbour today.
''It is just really striking to have two mothers and calves in the same area at the same time,'' said a spokeswoman for the Office of Environment and Heritage, Gabrielle Last.
''They are just playing really, really gently together, and exploring. They are mostly underwater.''
Hundreds of people spotted the whales from cliffs and foreshores around the harbour and northern beaches.
National Parks staff said they would be ready for the possible return of the whales today, and would keep boats or helicopters from approaching closely. A spokesman, Geoff Ross, said the whales needed a clear area of at least 300 metres around them.
''This mother with its brand new baby is using the sheltered waters of the harbour to avoid predators while the young calf gets its 'sea legs','' he said.
The agency encouraged people to report whale sightings on the twitter website, using the hashtag #whaleon.
Southern right whales are an endangered species, with about 10,000 surviving in Antarctic and southern waters. The whales off Sydney are not migrating north and are expected to return to Antarctica soon.