Premier Gladys Berejiklian has urged all Sydneysiders to be on high alert and use masks in crowded spaces, as the Northern Beaches COVID-19 outbreak expands to 28 people.
Approximately 250,000 people living in the Northern Beaches area have been told to stay at home for three days as testing is done.
Ms Berejiklian says the next few days will be critical in determining whether restrictions need to be re-introduced.
