BEIJING, Oct 20 (Reuters) - New home prices in China grew at a slightly slower monthly pace in September, data showed on Tuesday, weighed down by tightening measures in some big cities to curb a potential market bubble. Average new home prices in 70 major cities rose 0.4% in September from a month earlier, compared with a 0.6% increase in August, according to Reuters calculations based on data released by the National Bureau of Statistics. On an annual basis, home prices rose 4.6% in September, versus August’ s 4.8% expansion. The property market has been a major driver in China’s economic recovery, with home sales and investment growing at a robust pace in recent months after coronavirus lockdowns were lifted. But policymakers are concerned about the risks of speculation and overheating. Regulators have instituted new rules to control the level of liquidity in the real estate market and some major cities have tightened curbs on home purchases to rein in prices. (Reporting by Liangping Gao, Lusha Zhang and Ryan Woo. Editing by Gerry Doyle)