SAN FRANCISCO -- After defying industry trends in recent years, Apple is feeling the slowdown in global purchases of laptop and desktop computers.

New estimates from two industry research firms suggest Apple saw a decline of 4 to 8 per cent in Mac computer shipments during the second quarter, even as some of its bigger rivals managed to find growth in the PC business.

Apple enjoyed steady increases in Mac sales for most of 2014 and 2015, while the rest of the PC market was in a slump. Although big PC-makers usually sell more units, Apple's Macs tend to command both higher prices and consumer loyalty.

But Apple Inc. has been reporting a dip in Mac sales since the end of last year, and estimates released Monday suggest that trend is continuing.