TAIPEI, July 7 (Reuters) - Quanta Computer and Compal Electronics, the world's top two contract laptop PC makers, forecast a 20 percent or more jump in their third-quarter shipments from the second quarter, powered by demand from emerging markets and for low-cost PCs.

Quanta, which makes PCs for customers including Hewlett Packard and Dell, has yet to see a negative impact on its sales from the global economic slowdown, Vice President Elton Yang said on Monday.

"The main driver behind the rise is from low-cost PCs," he said at an investor event sponsored by the Taiwan stock exchange.

Compal attributed its strong outlook to growing laptop demand in China, India and eastern Europe, which would outweigh slowing U.S. demand, said Gary Lu, the company's chief financial officer.

Quanta and local rival Asustek Computer are expected to benefit from growing demand for low-cost PCs as a U.S.-led economic slowdown forces consumers to cut back on spending.

"The company (Quanta) is not being affected by the economic situation and rising manufacturing costs," Quanta's Yang said, adding Quanta's full-year target to ship 40 million laptops remained unchanged.

Last month, Quanta predicted global notebook PC shipments would grow 25 percent this year on healthy consumer demand, even though corporate demand was slipping.

It added it expected its own low-cost notebook shipments—one of its fastest growing segments—to hit around 10 million this year as top brands try to tap demand from emerging markets for 8-10 inch, cheaper PCs, known in the industry as Netbooks.

Shares of Quanta ended up 1.3 percent on Monday, roughly in line with 1.6 percent jump in the broader market . Compal's stock fell 0.6 percent.