A gauge of manufacturing in New York State unexpectedly fell to its lowest level in more than a year in September, the New York Federal Reserve said in a report Wednesday.

The New York Fed's "Empire State" general business conditions index slipped to 4.14 in September from 7.10 in August.

September's reading marked the lowest since July 2009. Economists polled by Reuters had expected a reading of 8.0 for September.

Employment gauges showed continued improvement. The index for the number of employees rose to 14.93 in September from 14.29 in August. The average employee workweek index increased to 7.46 from 7.14.

The index of business conditions six months ahead fell to 31.34 in September from 35.71 in August.

The survey of manufacturing plants in the state is one of the earliest monthly guideposts to U.S. factory conditions.