The headline composite output index rose unexpectedly to 56.7 in September from 55.7 in August. The expected score was 55.6.
Growth accelerated in both manufacturing and services, albeit with the former continuing to lead the expansion.
While service sector activity showed the largest rise since May, the increase in manufacturing output was the greatest since April 2011.
The services Purchasing Managers' Index increased to 55.6 from 54.7 in August. The score was forecast to rise slightly to 54.8.
At the same time, the factory PMI climbed to 58.2 from 57.4 a month ago, while it was forecast to fall to 57.2.
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