It sounds like a root fungus to me. A soil drench of fungicide, repeated in 2 weeks, may save it from getting worse. Until the roots start working again, the plant cannot take up moisture to feed the leaves (and push open the buds). The plant will shed leaves as a survival instinct to stay alive, keeping the moisture in the trunk. Once the root problem is stabilized, the leaves will come back. The only other thing you can do is cross your fingers and say your prayers. If the problem isn't corrected, the plant will die slowly.

I think you could watering it more. A root fungus means yellow leaves for me.

Is it in soil or in a container ?

For flowering, it's early? What kind of camellia is it ?

The symptoms of a severe root fungus are the same symptoms as drought. The leaves begin wilting and fall off, while still green, because the roots have quit working. One's first reaction often is to give it more water, which can be the worst thing to do. (I have learned the hard way.) But in arid conditions like San Diego, it may indeed be dry conditions. Scratch the bark to see if it is green and viable, both on the trunk but also out on some of the smaller barren limbs. If in doubt, it would not hurt the the plant to apply a soil drench of fungicide as a precaution.

There are so many "if"s about your situation. If it is caused by dehydration. Watering is the key. If the plant is in ground. You need to use a thin stick to open up the dry root area( water will not penetrate the dry mass) to let water thoroughly reaching the roots. If the plant is in a large pot. You can find a large trash can to soak the dry root mass for about one hour.

If the root is very wet already, root rot can be a tough issue. I am very sure you can do some common sense investigation to find out the possibility of dehydration or root fungus. I hope your plant problem is only water.