Factory activity in the U.S. mid-Atlantic region slowed in November, dropping to its lowest since May, a survey showed on Thursday.

The Philadelphia Federal Reserve Bank said its business activity index dropped to 6.5 in the latest month, from 19.8 in October. This month's figure was well below economist expectations for a reading of 15.0.

Despite the drop, the survey has been positive for six straight months. Any reading above zero indicates manufacturing expansion in the region, which includes factories in eastern Pennsylvania, southern New Jersey and Delaware.

The new orders index fell to 11.8 from 27.5 in October, while employment sank to 1.1 from 15.4. Prices paid rose to 29.9 from 21.7.

The survey showed a waning in optimism about the future, with the six-month business conditions index falling to 45.8 from 60.8, which was the highest since September 2003.

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.