Factory activity in the U.S. mid-Atlantic region increased by the most in more than two years in September and firms' optimism about the future hit a 10-year high, a survey showed on Thursday.

The Philadelphia Federal Reserve Bank said its business activity index jumped to 22.3 in September, the highest since March of 2011, from 9.3 in August, easily beating economists' expectations for a reading of 10.0.

Any reading above zero indicates expansion in the region's manufacturing. The survey covers factories in eastern Pennsylvania, southern New Jersey and Delaware.

The new orders index rose vaulted to 21.2 form 5.3, while employment rose to 10.3 from 3.5. Prices paid also rose, climbing to 25.3 from 17.30.

The survey showed respondents were also unusually optimistic about the future, with the six-month business conditions index jumping to 58.2, the highest since September 2003, from 38.9 in August.

The survey is one of the first monthly indicators of the health of U.S. manufacturing leading up to the national report by the Institute for Supply Management.