TOKYO (Reuters) - Canon Inc said on Monday it would sell its first mirrorless camera from mid-September in a bid to tap a growing market for small, interchangeable-lens cameras that rival Nikon Corp entered last year.

Canon will manufacture 100,000 of the cameras a month, the company said in a statement.

Mirrorless models have large sensors, providing good picture quality, but no optical viewfinders. That enables manufacturers to keep the camera body smaller and lighter.

In Japan, where consumers tend to value easily portable products, mirrorless cameras account for around a third of all interchangeable lens models. In the United States, their market share is closer to a tenth.

Canon's move will ratchet up competition with Nikon, its main rival for hefty single-lens reflex cameras used by professional photographers and enthusiasts.

Shares of Canon were down 3 percent and Nikon was 2.6 percent lower on Monday afternoon, underperforming Tokyo's broad Topix index, which lost 0.9 percent.

(Reporting by Reiji Murai, writing by Tim Kelly; Editing by Chris Gallagher)