BEIJING, May 17 (Reuters) - Real estate investment in China rose 21.6% in the first four months of 2021 from a year earlier, cooling from a 25.6% gain seen in the first three months, official data showed on Monday. Property sales by floor area grew 48.1% year-on-year, slowing from a 63.8% rise in the first quarter of the year, the National Bureau of Statistics (NBS) said in a statement. New construction starts measured by floor area rose 12.8% from a year earlier, compared with 28.2% growth in the January-March period. Reporting by Judy Hua and Kevin Yao; Editing by Sam Holmes Our Standards: The Thomson Reuters Trust Principles.