Demand for air freight, a leading indicator for the strength of world trade, is set to slow in the rest of 2010 and 2011, the International Air Transport Association said on Monday.

In a snapshot of the cargo industry, IATA said air freight markets were starting to cool off after a rapid post-recession rebound, with purchasing managers less optimistic and planning to ship fewer goods by air.

"All key indicators for air freight demand are now pointing to slower demand growth in the rest of this year and 2011," the Geneva-based industry group said. "The surge in air freight in Asia and South America is now slowing."

The need for speedy deliveries when the global economy began to rebound boosted air freight in 2009 and early 2010, according to IATA.

"That process appears to be coming to an end," it said of the surge in demand, forecasting growth of air freight would slow to 6-7 percent in annualized terms later this year and in 2011.

Many high-tech products such as laptops are increasingly being shipped by ocean not air, but semi-conductors are still being flown to their final destination, the IATA report said.