As of noon on Monday the patients, ranging in age from 18 to 67 years, were receiving treatment from the WNSWLHD.

Ten of the patients are believed to have acquired the virus overseas, one is known to have had close contact with the confirmed cases and it's unknown how the additional case was contracted.

According to a spokesperson from WNSWLHD all cases, contacts have been followed up and tested where appropriate, and the people involved have either entered home isolation or have completed home isolation.

"NSW Health wishes to thank all those individuals for their co-operation," the spokesperson said.

"Any new case and their close contacts will similarly be asked to self-isolate unless hospitalisation is required.

"Those affected are contacted every day to check that they are well. "

The health service is reminding all travellers returning or arriving from overseas to self-isolate for 14 days even if you have no symptoms.

"Please follow the home isolation guidance," the spokesperson said.

"NSW Health is continuing to trace and respond to cases as they are diagnosed to slow any spread of COVID-19 in the community.

"To help protect the community people are asked to: . clean your hands thoroughly for at least 20 seconds with soap and water, or an alcohol-based hand rub . cover your nose and mouth when coughing and sneezing with tissue or a flexed elbow . avoid close contact with anyone with cold or flu-like symptoms . stay home if you are sick . keep your distance from others as much as possible through social distancing."

For advice and information about COVID-19 visit: www.health.nsw.gov.au/Infectious/diseases/Pages/coronavirus.aspx