Moody's on Thursday cut China's crisis-hit property sector's outlook to negative from stable, citing economic growth challenges the ratings agency said would dampen sales despite government support.

Moody's said it expected contracted sales to fall by about 5% over the next six to 12 months in China, and the impact of government measures to boost property purchases was likely to be short-lived and uneven.

The outlook downgrade comes amid a string of debt defaults by cash-squeezed developers. China Evergrande Group, the world's most indebted property developer, is at the centre of the crisis.

The crisis has also engulfed China's largest private property developer Country Garden Holdings Co, which has been battling to avoid a default, having won approval from its creditors this week to extend the maturity of several onshore bonds.

Credit stress at Country Garden, which Moody's rates as Ca with a negative outlook, has amplified investors' risk aversion, Cedric Lai, an analyst at the agency said in a statement.

(Reporting by Dimpal Gulwani; Editing by Jacqueline Wong and Jamie Freed)