The Institute for Supply Management, a trade group of purchasing executives, says its gauge of industrial companies rose to 59.6 in March from 56.5 in February. It is the eighth straight month of expansion.
Economists polled by Thomson Reuters had expected the measure to read 57. A level above 50 indicates growth.
Factories are boosting production for exports and their customers are slowing the drawdown of their inventories, helping power the economic recovery worldwide.
Manufacturing surveys Thursday in China, Britain and the 16 countries using the euro all showed factory activity surging.
