The new variant, which originated from South Africa, is now spreading in the area but with only a small number of cases so far.
Lucy Hubber, public health director for Nottingham, said there were nine cases in the city.
Jonathan Gribbin, public health director for Nottinghamshire, added there are currently two cases in the county.
Mrs Hubber said: “Those nine cases are not all connected to a single event – so that does support the idea of people picking it up from a number of different sources.”
There are no current cases of patients with the new variant in Nottinghamshire hospitals at this moment in time, according to the NHS Clinical Commissioning Group.
Mr Gribbin said: “Omicron spreads much more easier than the Delta variant and we have in Nottinghamshire already evidence of community transmission where there is no travel history.
“We are observing a doubling of cases nationally of the variant every two to three days. It is spreading very fast.”
Public health bosses stressed that people should get their jabs as well as boosters and adhere to restrictions including wearing face coverings on public transport.
New rules also mean a return of masks in most indoor public spaces including theatres and cinemas and, f rom Wednesday December 15 use of the NHS Covid Pass – proving vaccination status or a negative lateral flow test – for entry to certain venues.