Two women have been injured in a balcony collapse on Sydney's northern beaches.

Six people were on the Newport balcony for a baby shower when it gave away around 11:30pm (AEDT) yesterday.

Two people suffered minor injuries while the other are being treated for shock.

It comes two weeks when the balcony on a Lane Cove house gave way as a family held a dinner party.

In a separate incident, a 23-year-old woman fell from a Bondi apartment overnight.

The woman went to the apartment block's rooftop after realising she had locked herself out.

She then tried to lower herself into her lounge room window on the third floor, but fell, landing on a fence.

Inspector Chris Stiles says she broke her pelvis, but her injuries could have been much worse.