MILAN (Reuters) - The highly contagious Omicron coronavirus variant is spreading rapidly in Italy, the National Health Institute (ISS) said on Thursday, releasing preliminary data of a flash-survey showing it accounted for 28% of cases on Dec. 20.

       The previous survey showed Omicron at just 0.19% of cases on Dec. 6.

       Comparison of the two reports shows the variant's doubling time is about two days, in line with the pattern already found in other European countries, ISS said.

       "Although the results are still preliminary, the estimate confirms the great speed of diffusion of the variant, which is set to become dominant in a short period of time," ISS President Silvio Brusaferro said.

       The data were provided in the morning to the government, which is expected to decide at a cabinet meeting later on Thursday on new measures to tackle the pandemic.

       The analysis is based on about 2,000 swabs collected in 18 Italian regions and the final results will be published on Dec. 29, the ISS said, adding a new flash-survey would be carried out on Jan. 3.

       Italy, the first Western country to be hit by the COVID-19 pandemic early last year, has seen new infections and deaths rising in recent weeks, but daily caseloads remain well below some other European countries such as Britain and Germany.

       Italy reported 146 coronavirus-related deaths on Wednesday against 153 the day before, while the daily tally of new infections rose to 36,293 from 30,798.

       (Reporting by Emilio Parodi Editing by Mark Potter)