How to cut a large sprite png into smaller UIImages?

For example, the png file is 1200 (h) x 50 (w) pixels, how can I cut the png and loads in 6 UIImages, each 200 (h) x 50 (w). Thanks!

EDIT - thanks to Michal's answer, the final code:

 CGImageRef imageToSplit = [UIImage imageNamed:@"huge.png"].CGImage;
 CGImageRef partOfImageAsCG = CGImageCreateWithImageInRect(imageToSplit, CGRectMake(0, 0, 50, 50));

 UIImage *partOfImage = [UIImage imageWithCGImage:partOfImageAsCG]; 
 // ...

 CGImageRelease(partOfImageAsCG);