Mid-Atlantic manufacturers say business conditions were quite strong in August, according to a survey released Thursday by the Federal Reserve Bank of Philadelphia. Expectations jumped to highest reading in more than two decades.

The Philadelphia Fed's index of general business activity covering the regional factory sector unexpectedly jumped to 28.0 in August from 23.9 in July.

"The index has increased for three consecutive months and is at its highest reading since March 2011," the report said.

Economists surveyed by the Wall Street Journal expected the latest index to slow to 18.0. Readings under zero denote contraction, and above-zero readings denote expansion.

Last Friday, the New York Fed said manufacturing conditions in its state slowed in August, although the level remains high. Earlier Thursday, data-provider Markit said a jump in its flash reading of August manufacturing sentiment indicates activity is the strongest since April 2010.

The reports suggest the nation's manufacturing sector is doing well in the third quarter.

Within the Philadelphia Fed survey, the subindexes generally were expansionary but more subdued this month.

The new orders index fell to 14.7 after it almost doubled to 34.2 from 16.8 in July. The shipments index dropped to 16.5 from 34.2.

The employees index fell to 9.1 from 12.2 last month. The workweek index edged up to 13.3 from 12.5.

Philadelphia area manufacturers are seeing some cost relief. The prices-paid index declined to 24.9 in August from 34.7 in July. The prices-received index fell sharply to 4.2 from 16.8 last month.

Philadelphia manufacturers are very upbeat about the next six months.

The general business expectations index increased to 66.4 from 58.1 in July. The Philadelphia Fed said it was the highest reading since June 1992.

The expected employment index slowed to 24.7 from 29.1.