A graphics processing system can divide a render output into plural larger patches, with each larger patch encompassing plural smaller patches. A rasteriser of the system tests a larger patch against a primitive to be processed to determine if the primitive covers the larger patch. When it is determined that the primitive only partially covers the larger patch, the larger patch is sub-divided into plural smaller patches and at least one of the smaller patches is re-tested against the primitive. Conversely, when it is determined that the primitive completely covers the larger patch, the larger patch is output from the rasteriser in respect of the primitive for processing by a subsequent stage, of the graphics processing system. The system can provide efficient, hierarchal, processing of primitives, whilst helping to prevent the output of the rasteriser from becoming blocked.