A serious case of Botrytis or "bud rot".
Removing all of it ASAP is the only way to combat it. Try and make sure you do not touch any clean buds with dirty fingers, this may spread it easily. This mould is caused by flowers that have too much moisture in them, which then causes them to "sweat" during warm conditions or dense flowers that have been rained upon or moistened some other way. These things cause a "super humid" atmosphere within the flowers and an ideal incubation site for the Botrytis mould to multiply and cause the damage you now have. Often, the first sign of this mould is a random leaf dying for no apparent reason.
At this stage, cutting as much away as possible may slow its spread and checking thoroughly when harvesting to make sure any other flowers that have mould are dried in another area to your unaffected buds will help stop the mould spreading.
Great air circulation and a dry atmosphere will be essential for the future maturation of your plant to stop the mould spreading, also when drying.
Sad as it may seem, removing a lot of buds that are infected or next to the effected buds is the only way to prevent even more buds going mouldy. This highlights how important it is to have a low humidity in your grow space during flowering and why keeping the buds dry is essential. Unfortunately Botrytis spores are everywhere and can not be eradicated by home gardeners, the spores are always "looking" for an opportunistic situation that will let them flourish, and deep inside moist and warm dense buds is their ideal breeding ground. Low humidity, lower water application and keeping your flowers dry are the only tools to fight Botrytis for the home gardener. Now that you have it, removal is the only way to prevent further progression.
Hope this helps,..............
Organoman.