Competition from Apple Inc.'s (AAPL) iPad tablet device is taking a toll on the global PC market, with shipments of desktops and notebooks in the first quarter declining from the same period a year ago, according to IHS iSuppli.

"The rising number of tablet models on the market, along with certain high-profile product launches during the first quarter, caused confusion among consumers as to exactly how to view the tablet platform relative to the PC platform," said Matthew Wilkins, an analyst at IHS iSuppli.

The researcher was the latest to note top computer makers are facing challenges as tablet computers attract the interest of consumers and corporations, a trend that led to disappointing global shipments of PCs during the first three months of 2011.

IHS iSuppli on Tuesday reported worldwide PC shipments totaled 81.3 million units in the first quarter, down 0.3% from a year ago. The researcher said three of the world's top five PC makers--Hewlett-Packard Co. (HPQ), Dell Inc. (DELL) and Acer Inc. (ASIYF, 2353.TW)--saw shipments decline from a year ago.

No. 3-ranked Acer, which sells a high proportion of netbook-type PCs that face a direct competitive threat from tablets, bore the brunt of the damage, with its shipments slumping by 20%, IHS iSuppli said.

Despite the first-quarter weakness, IHS iSuppli still expects PC sales will rise later this year, with the current forecast predicting the global PC market to rise 8% to 373 million units this year.

H-P continued its reign as the No. 1 PC vender during the quarter, followed by Dell. Rounding out the top five were Lenovo (LNVGY, 0992.HK) and Toshiba Corp. (TOSYY, 6502.TO).

   -By John Kell, Dow Jones Newswires; 212-416-2480; john.kell@dowjones.com