A survey shows China's manufacturing contracted by an unexpectedly large margin this month, adding to signs of economic weakness.

The preliminary version of the Caixin purchasing managers' index, formerly sponsored by HSBC Corp., fell to a 77-month low of 47.1 in August from July's 47.8 on a 100-point scale. Numbers below 50 indicate a contraction. That was weaker than most analysts expected.

The survey found output, new export orders and employment all declined at faster rates than in July.

He Fan, the chief economist for Caixin Insight Group, a Chinese financial publisher, said in a statement the index showed there is "still pressure on the front of maintaining growth rates."